Different mentality/goals I suspect. Personally I just like to ride with minimal hassle from the bike.
If I need more power I don't want to degrade MPG, longevity or ease of maintenance so I get something with a bigger motor.
The Mods I'm up to are aimed at saving a bit of electricity to run heated gloves, going to sliders & maybe a better clutch.
The later are aimed at reducing maintenance as much as being mild performance mods.
Far as Modified bikes go, I see a few around here, & there's normally a contingent of modd'ed bikes at the Ferry to Ferry run.
Most of these are modified 50cc Honda Ruckus, often with the extended rear to add a GY6 150+ variant engine.
I tend to keep away from them since they're usually running too rich so their exhaust is pretty dense & nasty to be near.
Some of the riders are reckless, but most seem to want to stay alive & intact so keep a leash on it in traffic.
Sometimes while out riding I come across a guy on what looks to be a Chinese brand scooter that has been modified for performance. It is very quick. Not sure of its top speed, but off the line is screams. Kind of cool to watch cause you don't expect that from a scooter.