Could someone help me understand why this stop was rejected so I can improve my submissions
For one, that’s a single family residence and therefore it’s not eligible.
Welcome to the forum 
This POI is not on the single-family residence. It is on the sidewalk. It shows on streetview in 2012 and 2024 and is clearly in an eligible location.
Was it rejected by “our team” or “the community”?
It was rejected by “our team”
Can you see a rejection reason in your wayfarer contributions (Niantic Wayfarer)?
It just says doesn’t fit criteria which doesn’t make sense to me as this is a historical marker
But that’s a modern structure? That woodwork does not date from 1790.
I hadn’t spotted that. It really doesn’t look like this is 230 years old.
I think it is eligible. It has the look of something that is temporary, since it is sitting on the sidewalk, but it has been there for years. I would reference the streetview years as evidence of its permanence in your supporting text. Also, check your information about it being from 1790 - maybe it replaces something else that was there?
Yes there might be some interesting history that goes with this. Some research could be in order.
It was recently refurbished by a local fireman but it was originally built in 1790
Ok sounds like a great story to tell. Be sure to include references in the supporting information, and it’s best if there’s no mention of any games. Wayfaring is about finding great places to explore, exercise or socialise.
You would want to add links for documentation of these claims because this looks to be made of wood, and as such cannot date back to 1790 in this form.
You say it has been renovated by a local, surely it would have been more official than that if it truly is a historically important local landmark as you claim?
I suggest you to find proof to this claim. Otherwise people wont believe it because of its look. web link will be best. Its permanence is also questionable because its missing between 2012 and 2023. Can you find out what happen in those years?
There is literally a plaque in the background with its date on it and easily googled
The house behind it there was built in 1774 out of wood and is still standing. Most houses in this neighborhood date back to the 1800s
In that case, use the web submit at Niantic Wayfarer, include a photo of that plaque as an extra supporting photo, use the supporting text to explain this plaque is for this structure and include helpful links (if there are any).
Why is there no mention of that in the submission? Best not to make reviewers do their own googling - putting the required references into your nomination will give a much better chance of success.
With something like this, it might be easier to submit with the plaque as the initial photo, and add a new main photo later to show the item with the plaque if you prefer. Or use web submit to show both if that’s better.
What you need is bring all this information to reviewer. Put yourself in reviewer point of view . Are you sure reviewer can google that information? You know a lot about the pump, but reviewer dont. Personally i wont take risk and would rather insert that information so reviewer dont need to dig information.