The benefit of a website like Patreon is reducing friction for small transactions like this. If you're going to put in lots of time and effort to convince one person to give you a million dollars, you can probably get them to write you a check more easily than you could get them to pay through Patreon But For Whales.
It'd be more lucrative for a patronage website to allow someone to go after big whales.
Just imagine if someone got a 1 million dollar grant. Even if it took a long time to secure it, it'd be a lot better than convincing 200,000 ppl for $5.