Spend hours picking photos and putting together a profile. Now for each person you have sex with, imagine you spent another 5 hours swiping, yet another 5 hours getting maybe 20 conversations going, which turn into 5 actual first dates (budget 5 hours each for prep, transportation, cancelling and rescheduling, etc.), assume 3 of them have zero chemistry, the other 2 are cool but the chances that someone will sleep with you on a first date is very rare, you go on a second date with them both but again no sex this time just for practical reasons (it's a weeknight, they work early, it takes an hour to get home), it fizzles out with one (no third date), the second one has a vacation planned, but three weeks later you finally have a third date and sleep together.
Mission accomplished. Probably a total investment of 40-60 hours across 2 months. And this assumes you even live in an urban area in the first place where there are 10,000's of people your age to swipe through. You still call that "easily free"?
Contrary to what you might think, dating apps are not full of girls looking for a quick first-date hookup. Sure, they're out there, but it's extremely rare that you'll a) find one at all, b) that she wants to hook up with you, c) that you actually meet and it actually happens. Just the reality of things.
By the way, this is also why the narrative of dating apps killing relationships is false. By the time you've put in 60 hours finding someone you're compatible with, you hope to god you can keep going out with them, instead of going back to square one and doing it all over again. Dating apps are work.