Honestly, the £5 a month you were giving them is probably less than the cost of special casing you in their largely automated donor marketing systems so this is a net win to both of you.
And yet it's worth it for them to have people canvassing door-to-door for those £5 a month donations with a <10% conversion rate. I guess the difference is that those people don't get paid, and the administrators do.
EDIT: Unless they literally don't care about the base rate donators at all. They only exist so that some of them will get converted into higher rate donators later.
