Hello,
First off, you are not submitting POIs to be stops/gyms, but rather Wayspots. Wayspots that get accepted are added to the Lightship map, which each Niantic game uses for game play locations. Each game has different density rules, such as Ingress having a 20 meter rule, and PoGo using S2 cells.
Second, the main photo could be better, since there is more to the sign than just the trail marker. I would either try to take a photo that is closer up to the main trail sign and try not to include the other signs. It would also help with to see the text at the top of the trail marker better, as even zooming in I have a hard time reading. I would also not take the photo at an angle, another reason why the sign is hard to read.
The supporting photo is good, as it shows all of the signs and the trail, and while Street View is from 2009 and doesn’t have the trail marker, it can be placed there easily with the supporting photo and Street View.
The title is also very unofficial sounding, translating to Cycle route 40 through the fields. I would still include Cycle Route 40, but include the text at the tope of the sign, as it better places the sign. You can include where the route goes through in the description instead.
Lastly, if there is a website that marks out the route of the trail, this would be good to include in the supporting info.
I take it that your rejection email said “out team,” not “our community,” which means ML, the AI, rejected it. ML has been rejecting more trail markers as of late, and I do agree with the rejection here, as there can be improvements made. I would try resubmitting after implementing some improvements, and if it’s rejected again, you do have the option to appeal to the Niantic team.