Most freerolls are crowded and action-packed, which increases variance.
When I have a large bankroll, I tend to play far fewer freerolls (except for those on CardChat) than usual, prioritizing paid games because they have a smaller field.
On the path to building my bankroll, I considerably increase the number of free games I play.
You can get an idea from the games offered by CardsChat daily. In total, counting the various platforms, we have more than 100 games per month, and that's incredible.
It's time-consuming, laborious, requires patience and, of course, constant improvement, but it is possible with a little dedication to build a decent bankroll to start in a solid way.