Also helps that gun go boom. Genre nicknames that stick tend to be snappy rather than descriptive. “Immersive sim”, “character action”, etc are terrible at describing what the game actually is. Regardless of whether or not the shooter is “for boomers”, a game calling itself a boomer shooter means, quickly, that it’s a fast movement shooter without “realism” mechanics like long reload times, usually with you using a vast arsenal of guns instead of only carrying a couple at a time and swapping them. Health kits or health-on-kill typically replace “take cover to regenerate HP/shields”.

Without using a -like suffix, there’s not really a snappy word that fully communicates that stuff, and as you say boomer=old. And -likes drift really far nowadays. Anything with parrying or drop loot on death is a soulslike. Anything with a run based structure and any procgen is a roguelike (even if the runs actually exist in a framework of permanent progression).