Ok, so reasons people like Goliaths.
Note that some of these reasons are about what they're not - but those sort of reasons are really important when it comes down to it, because people's red lines on what they don't want to play tend to be very strong in TT RPGs.
1. They fit the "Big Strong Race" archetype pretty much perfectly.
Not only are they one of the largest playable D&D races (if not the largest - 8' tall and 340lbs is the top of the range given, but we could easily envision one 9'+ if we allow 7' humans and so on), but they're always drawn as large and perfectly formed, and their mechanics and lore completely support this fantasy, rather than veering off in some other weird direction, as most large races do (Minotaurs and Firbolgs, for example, have odd mechanics and flavour).
2. They're
not a "beast race"/furry.
This might seem like an odd reason, but post-2E, most larger races in D&D have been animal-people or monster-people of various varieties, and a lot of players, in my experience, just aren't into that. For every player who loves the idea of playing Dragonborn or a Minotaur, for example, there's one who won't even consider it.
They're also not a robot. Robots have, I think, a broader appeal and create fewer raised eyebrows than beast-people, but still a lot of players would rather not be a robot.
3. They're fully humanoid/conventionally attractive.
@Paul Farquhar mentions he'd be excited if they were less humanoid, with a more "Hulk"-like physique, and I'm sure
some would agree (I would, for example) - but many others would disagree. A lot of people want to play a tall
attractive muscle-y Barbarian-type (and have it mechanically supported, which humans don't really, and there are some more complex issues around extremes of size and D&D races which are a whole other discussion - in short players are strangely reluctant to play a 7'2" or 3'4" human even though such people exist when other races which are naturally those sizes do).
Half-Orcs have the distinct problem that unless you basically say "I appear to be not be a Half-Orc", they're not conventionally attractive, with the typical tusks and so on. They may be "hot" or pretty cool-looking, but it's a lot more of a thing to be be-tusked and greenish than it is to have "kewl patternz" in monochrome on your skin.
4. +2 STR, +1 CON.
Not the only race with it, but the only conventionally attractive one (soz Mountain Dwarves, but some people think you're short and fat, unfair I know).
5. Backstory is pretty simple/limited, meaning it doesn't dominate the character, nor is likely to become an issue in a campaign or whatever.
Again with a lot of races, especially big/strong ones, there's some kind of serious backstory to them that means you can't just be who you want to be, or not easily, because you're dragging baggage. We've had DMs on here saying stuff about how they give Half-Orc PCs an extremely hard time, and thinking this is cool/normal.
The claims that the backstory is "very dark" are obviously laughable exaggeration, and at odds with the wide popularity of fictionalized portrayals of the Spartans and the like, who were known for the exact same stuff
and worse (non-fictional Spartans were far, far, far worse, of course), and it's not exactly uncommon in many ancient cultures to practice exposure (there's a reason it has a one-word name). Their philosophy is basically just a straightforward spin on "rugged individualism", and whilst that's not everyone's cup of tea, it's a hugely common one, especially in the US, and there's a reason people unironically like Ron Swanson. Plus it's exactly how many/most PCs operate anyway - attempting to be heroic, acting more as individuals than part of society (part of the PC group, sure, part of society? Rarely, in my experience - there's a reason Murderhobo is a thing, and even when it's turned down to Goldhobo or Justicehobo or the like...).
6. Solid mechanics.
Not worth dwelling on, and I've already mentioned that their mechanics are thematically spot-on to "big strong guys", in multiple ways, and perfectly suited to being STR-based melee combatants, but all their mechanics are solid and work decently and have some real-game applicability, even if you don't routinely check encumbrance, the boost there lets them move stuff that would take several normal adventurers. Mountain Born is the least useful but thematically appropriate. Sure, people will wish they had Darkvision, but such is life.
7. They actually have rules and are in 5E. Something that is not true of say, Half-Giants or Half-Ogres.
I hope this makes it all make a big more sense to those who "don't get it".
Personally, do I like them? No, they're kinda flexing gym-bunny mountain creeps, but I don't like Ron Swanson either (though the character is hysterical). Also one thing I strongly agree with
@Paul Farquhar on is that they have a dumb name. A really dumb name. But some aging people (including one of my players) watched the Gargoyles cartoon back in the day and think Goliath is an awesome name, not a lame and weirdly Biblical one. I can think of at least 5 PC races with dumber names off the top of my head, though. But I can understand why people would like them.
and yes, I intend to create a feat that allows to deal some damage with their stone spurs while rolling through an enemy's space.
