1) supposedly louder sounds better with all other things being equal which is what has precipitated the so called loudness war (wikipedia it!). also people want to crank sh*t up in the car while on the motorway or whatever which is why top40 chart pop gets the brickwall limiter treatment. i'm sure you know this already though and are just asking for people to turn it down a bit. which is fine maybe they should. personally i am not sure why chip people are so big on mastering stuff at all when all the music sounds just fine (or just bad) without it / played straight from the tracker. secretly i think like a lot of things we as chipsceners do it is to legitimize our stuff as "real music"
i have no real evidence for that but i know a lot of people are trying to distance what they do from videogames / 1990s finnish teenage nerd culture and maybe the "recording all the tracks separately into logic and then using plugins that you have to pay for to make them louder and more bassy" is a step on that path along with the having it put on vinyls and selling it for real money aspect
that is probably a bit cynical. the technical aspect of music production is quite enthralling and i bet some people just find it addictive or maybe even theraputic to do something clinical and scientific like that at the end of the artistic process. personally i'm crap at it which explains both why i don't do it and why i'm bitter about people who do
2) probably they are doing copy paste Compo Echo and are too lazy to fix it or maybe they just don't care? recently i like to use a fine pitch bend to separate out notes like that because skronky detune has always been lovely to me but the delay tip seems good too. mostly i just don't do compo echo, it's a cheap trick and not particularly artistic imo, although i am sure you can find loads of my songs where i've done it and probably even done the thing you complain about