I think you’re going to struggle with the memorial to a pet, because memorial nominations need to be good places to explore, primarily by offering information to support the notability of the person memorialized: Seating Benches (yes, I know this says benches, but it has guidelines applicable to memorials in general).
Regarding this:
I have seen some people just have photos of fire hydrants or random doors with no art or building and hem be accepted why it mine so different?
The criteria have changed and been clarified over time. Something that was accepted in 2019 might not be accepted today, but might not meet the criteria for removal either, leaving it on the map to confuse people like you. Fire hydrants, though, should be reported for removal as those can block emergency services.
If you’re looking for a shortlist of suggestions for types of places that might be eligible and sitting forgotten, I’ve got one here that might be helpful–though perhaps not perfectly applicable to your exact neighborhood: Great Wayspots "Left on the Ground"