lower elo trading off bishops?



Bishops are worth more in an open position and knights are better in closed positions. But beginners aren't thinking with that much depth. It's purely, "I can attack something and double the pawns".
At my very low level (about 400) I don't think it's just simplification. It's also fear of nasty long-distance pins and attacks. Once bitten by a long-distance bishop, twice shy of bishops. They're threatening! Meanwhile some people see knight forks easily, others don't, so if you're playing the latter, if you've got a knight there's a chance to snap up a few pieces... It's hard to assess the true relative values of bishop and knight because unless you're a good player, which is more valuable depends a lot on you as well as the position.

I am 1200 in rapid and 800 in blitz. People I play often take things on sight. They can't bear the tension. It makes for great traps and counter attacks if you can develop well off of it. Other times it is just dull and straight into an end game because all the pieces are off the board and the pawns have weaknesses on both sides. Not everyone does this. But it is quite common. I suspect they think of the trades as clearance sacrifices (even though they have failed to develop anything to follow up), or as damaging to pawn structures, if they know something of end games. But more than likely it is disruption to your development and they are hoping to be better with less on the board/ hoping you blunder under pressure.