For two reasons but I'm not one hundred precent sure, one being that people were getting pushy with wanting translations on the series and bugging the translators about it. The other reason being that the lines and gags were becoming way too complex and big to translate.
Third reason is that some of this stuff and some of the relationships here are really toxic. Having to translate it, to put some of this stuff into English, when it's a good shot that another part of, say, Marisa and Reimu is going to be same level of abusive relationship, that kinda saps energy out of translator.
