It's cause bl target audiences is Fujos and author create stories revolving around what's popular with Fujos. Just look at what the most popular BLs are and you'll figure out why ╥﹏╥
Is
Well fuck me ig lmao. Anyways, is bc more often than not BL authors jump to using sex as a plot device, is faster and easier to get views for them. Years ago starting your story with moans in the first panel would get you more attention, now they just took that and ran with it. Quite literally the industry is oversaturated with porn no plot stories, bc why bother making an interesting story when you can just make porn(¬⤙¬ )
Well bl have categories too. Yaoi or shounen, if u only read wats popular in bl most often than not it's smut.
Check out the sub categories that will tell you if the story focuses more on relationships than the sexual aspect.
Shoumen ai*
What @Miroro and @BakedPotato said are true, and/but also, gay men irl also are very quick to get physical. (Well I'm not a gay man, I'm a woman so I am not generalising gay men). But most men use Grindr or gay apps like that for a quick f*ck or casual. That's not to say that gay men don't exist who don't sleep around and all, it's that it's easier for men to get casual s*x and they like casual s*x (I suppose, since so many guys(straight, gay or bi) are DTF)
Unfortunately, smut sells in the BL community. Some slow burn stories I read people are always asking about when they're going to have sex without even considering the relationship is barely developed. Maybe that's why BL in general has such a bad rep and always referred to as 'porn' because let's be honest, many people DO want just the pwp sometimes and that's why they're so populaar.
Even on here too if you look at the numbers, shounen ai (fluffy BL) isn't as abundant as yaoi (smutty BL). There are only 5k BLs that are considered shounen ai, while nearly 16K BLs that are considered yaoi.
hetslop
The shounen ai is fluffy vs yaoi is pwp genre differentiation is more of an english-speaking fujo phenomenon. In Japan at least, everything falls under the BL genre umbrella. There are many plot-heavy, non-sex-focused BL, but they aren't what's popular atm and don't get as much visibility in EN spaces in terms of translations/scanlations. I think it's unfair to generalize, there's a lot of PWP in straight manhwa as well. It really just depends on where you look and what you're looking for.
Read shounen ai instead
What I've noticed that straight manhwa take their time building feelings and relationships, but most BLs jump straight into physical intimacy with barely any emotional buildup . Many bls 1st episode is them getting physical. Then they try to get to know each other and every other episode is them just doing stuff