Google has made it clear that they were going to completely phase out the “Classic” Google Maps (Q2 2015). The vast majority of feedback has been negative towards the new Maps (I have yet to see a single positive comment), but per their history (and company policy?), they have no intention of listening to user feedback, so all methods of accessing the old Maps have stopped working.

No URL query term, no cookie, no user-agent hack, or browser extension can be used to access it anymore because they completely removed it now (think they “fixed” the loopholes that allowed people to access the old version).

There are innumerable people complaining about this in countless threads on more sites than there are stars in the sky, but if Google keeps with its tradition of ignoring user feedback, then all of the petitions in the world won’t get them to bring it back. The best you can hope for is to send feedback about very specific issues and hope they actually bother to read it.