Neither of those reasons would surprise me.
This might be a generalization on my part... but Reason #1 sounds more in line with what a lot of late Gen X'ers think, and your average Marvel writer IS a late Gen X'er right now. Them disliking marriage because they got a bad taste of it from sitcoms growing up, and not from conservative beliefs or from some misguided idea that "marriage ends the story" like the BND boys, sounds believable to me if we just go by demographics.
Reason #2 sounds dumb, but not unlikely lol.
These reasons lead more credulity to my theory that OMD might get undone without it being officially undone. Spidey will defeat Mephisto, Peter and MJ will remember everything and get back together as a long-term couple but won't be legally married. Which isn't ideal, but honestly not bad. And seems like the parties that subscribe to these reasons would be okay too.