It doesn't. Brook boards always added like an extra $100 dollars to any custom or DIY fight stick. The reinvigoration came because sticks that used to be $250 new are now closer to $100 and in some cases less, particularly leverless controllers. If you've heard of the Haute 42 or any of the countless leverless controllers that have been flooding Ali Express, Amazon, and other sites they're possible because of the firmware gp2040. For a lot of these new makers all they have to do is get the pcb printed and build an enclosure.
I remember spending $75-$200 for MadCatz/Hori/... sticks when I was more involved with the fighting game scene around 10 years ago. Customizing an OEM stick or doing something DIY for an arcade cabinet was doable with a donor controller.
This all hangs on what "reinvigorated" means and I'm fine conceding the ground of not paying close attention in the intervening decade. I didn't think it was prohibitive back then, maybe it was in between then and now, and perhaps the barrier to entry is so low now that it's even better for gamers.
15 years ago it was maybe $50-$150. As recently as 4 years ago it was more like $200+ and hope for a sale. Top of the line around a decade ago was a madcatz te or razer panthera for $200. The DIY aspect and ease of changing internal parts got harder with most sticks released in the past 5 years.
Brook boards alleviated some of that but that was still an extra $50-$100 depending on the vendor and available supplies and some hardware hacking that a lot of people were unprepared to do. Those who were willing to hack were hit hard because most fight sticks were taken off the market from back then and people got a bug up their butt about value during lockdown these old fight sticks started showing up for as much as $400 on Craigslist or Facebook marketplace. A 9 year old panthera was being sold for as much as a brand new Victrix. The market was rough. It still is for secondhand fight sticks.
This is why gp2040 was reinvigorating. With cheap pcbs and ready made firmware came cheap controllers. $50 gets you a 3d printed leverless. $150 gets you an aluminum leverless. There are mini boards that are just keypads with thumb sticks running the same firmware as full sized fight sticks with dual analog levers. You’re starting to see the same explosion in ideas and customization we saw in the keyboard space like 8 years ago.
