As I tend to dial down to a 6 or 7 what I often feel D&D has cranked to 11, I often reduce the size of giants.
An 8-foot dude weighting close to a ton and wielding the equivalent of a 10-inch diameter baseball bat should be f*****g terrifying, there is no need to go all the way to 15-20 feet, nevermind 25-50 feet tall! Making them smaller helps me fit them better on an ecological and geopolitical scale, and hand-to-hand fighting against giants seems more believable than trying to kill with a sword something you can't conceivably hit above the knee.
I have similar feelings in modern or sci-fi RPG when someone is asked to go against a tank with a handgun. At this point the game (usually) shifts to putting the handgun away and try to lure the tank into a ditch or bog, or finding vulnerabilities, or crippling it's weapon etc; and you know that one solid hit is likely to kill you. In other words, you don't just keep firing at it until it explodes (though video games do that...). I'd expect a similar approach in D&D with giants 25+ feet tall; one true hit of it's sword should cut you in half, and it's likely to shrug anything you're gonna throw at it. So you need to find a way to bring it down, prevent it from running you over (or running away), and attack vulnerable points.
A 25-foot tall (or more) giant battle like this can be fun, just like battling a tank with nothing but a handgun, but it's something you'd bring once, maybe twice in a campaign. Downsizing giants allows me to to play the skirmish game without having to shift to a different battle paradigm and without stretching my willing suspension of disbelieve too too thin.