It wasn't for the heck of it. I know they had reasons, just not necessarily the ones in the video. And the reason I think that (beyond years of learned skepticism) is simply that the choices are inconsistent. Why are orcs and drow more important to keep as humanoids than goblins or bugbears? Why are kobolds dragons but dragonborn aren't? What creative explanation is there for that? How do those choices make the game better?
Okay, so you do know they had reasons, so your only complaint is that you either do not understand or do not like their reasons. That is different than what you keep saying.
AS to a stab at answering your questions, which given the history you will likely dismiss, here are some speculations.
1) Drow were explained along with elves, they have lived in the material plane long enough. They were not "more important" and in fact they have said nothing about Drow to date. Likely they were kept as humanoid because they are just elves. Elves that have a cult that worships an evil goddess. This doesn't make them that unique from normal elves. Normal elves can be evil and worship evil gods.
2) Orcs were kept as humanoid because they are being moved into being more like humans. I know, you hate that phrasing because orcs should never be human, but that has been a long long direction of DnD. There is a correlation between DnD orcs and Warhammer Orcs. Also, there is just no reason to NOT make them humanoid. Orcs were created by Tolkien and adapted to DnD. They have always been humanoid and they do not have the touch of otherness beyond their toughness.
3) Goblins and Bugbears are fey. Like, go find a Fairy Tale, goblins will be there. Goblins as dark fey is literally their most common interpretation across media. Scooby-Doo had Fey Goblins, The Labrynth had Fey Goblins. This is less about keeping them the way they are, and more about moving them into the place they actually belong within the wider cultural lens.
Why are points 1 thru 3 good for the game? Goblins are going to be more interesting and flesh out the feywild, that's good for the game because the Feywild actually lacked a threat like goblins. This also makes it easier to build connections between Goblins, Hobgoblins and Bugbears which sorely lacked them. I actually had split Bugbears into a fey creature years ago. Keeping elves consistent as humanoid descendants of fey keeps them as they have been for decades and keeps the PHB character options easier, same with Orcs.
4) Because Kobolds have a long history of being Dragons since 3.5 or older. Dragonborn are very Draconic, and you COULD make them dragons sure... but you aren't required to. I don't have a satisifactory answer of "what is the difference" but I didn't make the decision either. Again, it is likely that Dragonborn are in the PHB and Kobolds aren't. And maybe their are Dragonborn that are more Draconic and will have the Dragon type. They literally stated that any given statblock is not representative of the entire speices. So, maybe some Dragonborn will be Dragons, that's something that has been established by the designers. Why? Because that's how they've designed it.
What creative explanations are there? A lot. Maybe some Dragonborn are more or less deeply steeped in Draconic magic, while Kobolds were crafted from Dragons themselves. Maybe all the Dragonborn share their original origin and are humanoids altered by Divine Magic to be reborn with different bodies, but since they are individual it does not change their species type. Maybe Dragonborn are still a work in progress from the Dragons or Dragon Gods, maybe in Faerun the rejection of the Dragons and Dragon Gods made the Dragonborn reject their draconic power as well.
How is this better for the game? Mechanical consistency combined with narrative freedom.
