From what I have gathered on the L.W. Discord - which I also only regard as rumors at best:

• It is not a sophisticated attack.
• The attacker is persistent in switching avenues of attack upon closing them.
• The attacker has not switched strategies, yet.
• Probably asleep right now and unable to automate the above.

Typical salty scriptkiddie.

Motives might be:

• got banned and/or defederated for any reason (probably a good one) and seeking revenge
• disagreement over political stances
• disagreement over moderation policy
• disagreement over decentralised nature of the fediverse
• just because