@Ironclad
Because they COULDN'T take it from the Commoner's Guild. They were going to kill the rest of her adventurers if she didn't agree to sign over everything to the Nobles, take all the blame, and become their puppet. They held her guild and guildmates hostage. In return they didn't send Tanaka to go kill the remaining few adventurers, but they erased her memory of pretty much everything so she couldn't tell anyone of the rotten deal, then they shut down the Commoner's Guild and sent Tanaka over to kill anyone left anyway.
Then they made her and her guild out to be insurrectionists to legitimize everything that was happening.
As for the stone, they needed to get it back to rejoin her with her memories. If the stone vanished first she'd be stuck like that forever or until she killed herself. Thus getting it back ASAP was priority #1.
The MC is shown to care about HER to some degree, just not overly so. The reason why is one that mystifies me, as well. Apparently in Japan/China/Korea, LNs/manga/manhua/manhwa an aggressive woman is treated as though she's insane, or dangerous, or distasteful. If the woman wants you and pursues you, is physically affectionate and such - she's bad, stay away from her. The LESS she wants you and more soft and weak she seems to be, the more you're supposed to lust after her and pursue her and make her want you. ... Seems kinda rapey, to me, but it's the
majority of every story I've read that's like this. The more a woman wants the MC, the more she gets ignored, double that if she's not incompetent and has some self-confidence.