First of all, while both series are owned by the same publisher, both are in different magazines. Rent-a-GF is Weekly Shonen Magazine, this is Weekly Young Magazine. The former is shonen while the latter is seinen, and they both have their own criteria for what series succeed and which don’t.
I think this series just hasn’t hit Young Mag’s particular sales threshold. It may sell okay, but not the numbers they expected. This can cause even the best manga out there to be cancelled - unfortunately, manga publishing is still very much a violent state of affairs.
But for the “WHY DOES MY FAVORITE MANGA GET CANCELLED WHILE RENT-A-GIRLFRIEND GETS A BAMILLION CHAPTERS” spiel that I see every time a series gets canned, I will simply say this - the fact that people still meme on Rent-a-Girlfriend, that it still garners discussion after nothingburger chapter after nothingburger chapter, that people still watch the anime even knowing what will happen in the future? Any publisher would nut their pants for a series like that.
If the manga fandom wants to stop Rent-a-Girlfriend, they need to collectively not give a shit about it. Don’t read it, don’t watch it, don’t buy it - even as a joke. And if you meet someone who unironically likes Rent-a-Girlfriend, then tell them to do the same.