SWF is extremely compact, since it was intended to be used over a dialup connection. Flash worked because the player was preinstalled on the computer.
The newer Ruffle player is a 10MB download in addition to the actual flash file. You get a new freshly downloaded copy of Ruffle from every site that's hosting Flash content.
The internet has very much moved on.
A three minute, 1080p YouTube music video encoded in AV1 video with Opus audio is 30 megabytes. No one bats an eyelash at downloading that.
To prove it, this one has been downloaded 2.6 billion times: https://www.youtube.com/watch?v=ekr2nIex040
To even further prove it, this one has been downloaded 17 billion times: https://www.youtube.com/watch?v=XqZsoesa55w
But compared to the average internet user’s connection speed or their consumed bandwidth at this time, 10MB is probably smaller. We just don’t put it in a plugin today because the browser cache can handle that just fine, and because it means the code is more sandboxed, and that if it needs updates, managing that is easy for the game publisher to do.