First, making the party take 20 on every square makes the game extremely boring, in my opinion.
There were a few times my party was extremely cautious listening to doors and examining them. It was so slow... Then I started just opening the doors before they could examine them... Just 1 or 2 exploded... but my saving throws saved me

It made the game a lot faster and exciting!
Second, if the traps are in random places, where the party is supposed to walk through, why don't they affect the monsters? They should also be taking 20 to walk through the dungeon... Even if they built the traps.. because I think there's always at least one of them stupid enough to blow them all
But then again, if there's the same chance to find treasure as to find traps, the players will take 20 happier than if they're just avoiding traps.
And if the objective is to search for something in the dungeon, more than fighting, then it makes sense to walk slowly.
About the 15 minute workdays, I've never thought about it before... I think I've never experienced it.
Maybe it's just a question of play style of players and GM,