Has it ever been any different? Except that manufacturers like BMW now get more of what was the 'tuning' aftermarket. BMW have opted for a share in that lucrative market. Why not, when a lot of the kit is on PCP finance. It's helping BMW's bottom line.
Go back to my younger days we were adding parts to make our cars more individual, (even without the 'go faster' stripes).
I ran a Cortina Mk 2 GT with an aftermarket set of 5 1/2" J steel wheels, Peco 'twin' exhaust, wing mounted racing mirrors and the obligatory Moto-Lita 3-spoke leather rimmed steering wheel.
Personally I like the production look to a car, like I did way back with my Triumph Dolomite Sprint. With its factory fitted 'add-ons', like the extra Sprint specific badges, front spoiler, twin pipe exhaust, vinyl roof, etc.. But many tried to make the less powerful Dolomites like the Sprint. I'm afraid I did find that approach a bit tacky.
I sense as so many BMWs these days are M-Sport models, (common as muck), is a reason some users, whatever the engine, feel the need to personalise them, to make it a bit 'special' and different.
Trying to make a 318d look like an M3, that (to me) is a different issue. But even that if done well, and viewed as an M3 Lite, has its place.
I wouldn't do it, but each to his own, not all BMW users (even enthusiasts) can get into the real deal.