It seems like every time I check twitter, product hunt and even this site, it seems like so many people are starting a newsletter. Much more than ever before. It seems like how it was back a few years ago how everyone was starting a podcast. Why are people doing this and why now?
Because "it is the time to do it"TM. And just like you said, exactly like when everyone was doing a podcast, or everyone had a blog.
Since most of the time activities prioritised not what makes sense but because" everyone is doing it". This kind of stuff reminds me the infamous orange square of Fyre Festival. A lot of people just posted that "because all the cool kids are doing it".
Newsletters are now in their "fad moment". People are doing it not because "it makes sense" (even though they will say they do it because it makes sense, but that's rationalisation) but because of its popularity.
Because I am sure as hell it doesn't make sense (as in ROI) for all the target markets/niches/etc.
Newsletters have been a thing for the last couple years.
I'm subscribed to loads of them. I want interested content delivered to me instead of me searching for it.
And, newsletters are great businesses.
PS. I'm also working on launching a newsletter : rippedrich.com