Your question, 'Are all infinite sums not divergent?' (revision history, timeline), was migrated to the Mathematics Stack Exchange site, and it is available here, along with both of its answers. There is no useful or reasonable sense of the word "deleted" that applies to this question. It has simply been moved to a place where, in the opinion of a quorum of 3k+ rep users of this site, it is more likely to receive appropriate attention and good answers.
To be clear, questions on regularization (along with many other topics of mathematical physics) are on-topic on this site. However, not all questions on mathematical physics (including regularization) are on-topic.
As an extreme case, if a question asks for a proof of a general mathematical statement and it is completely devoid of physics context, then it is best posted on the maths site. As another extreme case, if a question deals with the application of a specific mathematical tool to a given physical problem, then it is clearly on topic here. In between the two there is a large gray area.
Some previous discussions in this meta site on where the line should be drawn inside this gray area are
Please have a careful look at the opinions voiced in those posts (and this applies to everyone reading this post, OP, mods and 3kers alike). It is also important to note that opinions on this topic are very divided, with many posts at score 0 through routes like +5-5 or more. You can see the upvote/downvote breakdown of a score by clicking on the score if you're 1k-rep or above (for performance reasons); if you can't do that yet you can use this SEDE query (using the post Id, the first number in the url from the share button), or this, this or this userscripts.
In general, if a question is purely about mathematical aspects of a mathematical tool or topic, it is generally considered off-topic here (i.e. it is migrated to the maths site, not deleted), regardless of how applicable it is to physics. (As an extreme example, linear algebra is useful for physics, but questions exclusively about linear algebra are off-topic here. Similarly so with other tools of mathematical physics.) Personally, I feel your question is squarely in that category.
(There are some questions, on the other hand, where the topic is mathematics but there are various reasons to expect that physicists would be better equipped to answer the question, and there is some debate on whether those should be migrated or not. However, I don't think this applies at all to your question, which explicitly thanks a mathematician for its foundation.)
As an aside, it is important to realize that most of the moderation on this site is not performed by the formal moderators (which are identified by a ♦ after their username, together with Stack Exchange team members). For details, see A theory of moderation, but the short story is that most question closures and migrations are community actions, and they require the agreement of five community members. Blaming "a moderator" for things like this is simply not helpful - particularly when question closures and migrations are openly and clearly attributed. (In particular, if a question is migrated, go to the page on the new site, look for the banner that says, 'migrated from $site', and click on the $site link.) Other useful tools for inspecting the moderation history of a post are the revision history (https://physics.stackexchange.com/posts/$PostId/revisions) and the post timeline (https://physics.stackexchange.com/posts/$PostId/timeline).
