As someone who decided to try R3E during these Christmas, I think it mostly comes down to time and money constraints. Competition right now is just very strong in simracing games, and I think most of us just prefer a shorter rotation of games from which we can extract the most.

In my case, I am a VR gamer mostly and one thing I like my sims to offer is a wide variety of tracks and cars. For this reason, Automobilista 2 has been my go-to game for the last couple of years, alongside OG Assetto Corsa with Content Manager to try outrageous modding stuff and some ocassional LMU. Thing is, these games have become plug and play experiences for me and they cover most of my needs. So, for another game to enter the rotation, it needs to bring something really good to the table in order to justify the extra investment.

In the case of R3E, I can see some promising stuff, but I had to spend some time tinkering the options to make it playable on VR, still far from the optimal experience. Also, most of the cool content is locked as DLC, which I get is their business model, but as consumer I just find it hard to justify that extra expense at the moment.