When I looked into installing mastodon, it was extremely resource intensive and required a bleeding-edge version of Rust, so I went with GnuSocial instead. That supports ostatus, but not ActivityPub, so it federates with fewer and fewer hosts.
I could install pleroma, which has some issues, but is a lightweight design I could actually support, but many mastodon users block all those instances anyway.
tl;dr Masto is hard to install and expensive to run. Partisans hate the alternatives.
The original server operated by the Mastodon gGmbH non-profit