yet you can keep dormant UTXOs for a long time without worrying about it. it all depends on what your main uses are with the money that you get

most people who get paid in bitcoin need to send it to an exchange or a dealer to get fiat anyway and can direct different UTXOs to different destinations

mixing everything you get right away is too wasteful and most people will not know how to not link their funds again after the mix

it's not as trivial as "just mix everything"