I mean renovating your house is not B2B so it makes sense they want business registration.
I think they do it because they don't want to bother with small buyers. If people knew how much cheaper the parts are in these companies compared to hobby markets they would all want to buy few pieces to save money. This is not customer they want, they want customers that buy massive quantities.
The one that rejected me was a supplier that generally targets larger full construction sites so I totally get it for them. For the rest though, their main audience is definitely normal renovation contractors, and my order sizes are exactly the same as those.
I think they do it because they don't want to bother with small buyers. If people knew how much cheaper the parts are in these companies compared to hobby markets they would all want to buy few pieces to save money. This is not customer they want, they want customers that buy massive quantities.