I have applied for lots of sits.
Some with very few applicants, some with 50+.
I would not put a limit on the number of applicants.
Everyone deserves a chance.
I worked out once that there are at least 40,000 members of THS.
A lot of the members of this forum who are sitters are full time or sit several times a year.
So they are on the website every day, checking sits.
I would imagine that most HO use the site less, maybe once or twice a year on average, so if they post a sit, unless it is short notice, are planning their vacation/travel well in advance, so there is no real rush to choose a sitter, in fact, are probably happy to get loads of applicants and then choose the most suitable closer to the date they are due to travel.
And then there are sitters who maybe only use the site once or twice a year, as their annual holiday - if there was a limit on applicants that would almost certainly rule them out.