When asking for an extension to submit revisions, should I mention that I am no longer in academia? I submitted a paper to a journal 6 months ago.
I finally heard back from them now,
and they would like revisions in 6 weeks;
for another round of review.

Since submitting that paper, I've submitted my phd thesis (which is now being examined) and am working full time in industry.

I plan to ask for an extension, for several reasons.
Including that it is the holiday season and my coauthors (supervisors) are all going on leave, as am I.

I am wondering if I should also mention that since I am in industry now, I have fairly limitted time in which I am able to work on revising my own papers.

On the one hand is is utterly true, on the other hand perhaps it is irelveant.

In general it seems like asking for an extention is probably not a big deal, since having been in review for 6 months, it doesn't seem like it would make much difference it it is finally published in 2 months vs 3 or 4 months.
Since plenty of people in academia also have limitted time to work on revising old papers (be it for teaching or for new projects).
Politely ask for an extension, keep it short, don't give reasons. Editors appreciate how hectic life can be and regularly grant extensions (without needing to know author-specific circumstances).