This is a great question and if I had some way of boosting it I would.
The costs of getting online with these services was pretty high.
https://news.ycombinator.com/item?id=3087928
Compuserve, charging $11 per hour, had "more than 250,000 subscribers".
Delphi, charging $6 per hour had a loyal but small (less than 10,000 users) following.
$11 in 1988 is about $23 today.