We do play with encumbrance, but the weight limit is so absurdly high it doesn't matter. Like, they even state in the rule
"Carrying Capacity. Your carrying capacity is your Strength score multiplied by 15. This is the weight (in pounds) that you can carry, which is high enough that most characters don't usually have to worry about it"
It's a rule designed specifically to not be used, even when its used.
Now, I have played games where it does matter. Star Wars has a pretty restrictive weight limit, Pathfinder to some degree, but D&D says "yeah, that 8 Strength couch potato? They can carry 120 pounds without being slowed down at all, no problem!"