I started using Meteor in 2014. I was active for two years, posting frequently on their forums, writing packages, building MVPs, etc. As I started building more things with Meteor, I realized that it doesn't scale well. It's great for proof-of-concept work. Frameworks can be incredibly productive for low-scale work, but they are painful to scale. No framework that can be simultaneously optimized for every use-case. Now, I always DIY with a router like Express.

Meteor's problems were rooted in its real-time protocol, DDP, which had some problems. Firstly, everything is real-time by default. It's better to minimize the amount of real-time components in your application as there are very few things that need to be real-time. Secondly, the pub-sub caching mechanism made it infeasible for situations with many concurrent users. I was able to get around this by proxying some of their internal functions.

Significant people in the ecosystem started leaving (e.g. Arunoda), probably for the same reasons. AFAIK, it's still the best JavaScript framework out there for prototyping and MVPs. Their accounts system makes whipping up a user-driven application trivial. MDG (the phenomenal team behind Meteor) is likely focusing their efforts on Apollo now, because they understand DDP's shortcomings. If you're interested in Meteor, I suggest looking into Apollo.