It's still very early. RIPE and ARIN have only supported publishing them for a few months. ARIN made very little noise about it during the rollout, and many networks are probably still unaware. Give it a couple years, and I expect we'll see fairly good adoption among those already publishing ROAs. There will still be the never-RPKI holdouts, however.

HE publishes their full ASPA table here, if you're interested in digging in: https://routing.he.net/?cmd=display_aspa_table