よ can be roughly translated as “didn’t you know”. From my experience with reading as well as looking over some grammar guides, it is meant to put emphasis by reminding the other person of the situation. “Reminding” not really being a memory recollection thing as a more of an agreement that this is the situation. Your sentence in particularly, the よ would be used by the individual to subtly bring them to their point of view and establishing a sort of common knowledge. Compared to the sentences without the よ, which would just be a statement that they are busy. With it, a common understanding is established.
It’s a little hard to explain, and the “didn’t you know” English phrase, in my opinion, captures the feelings of よ more clearly than my previous explanation. Not really an expert, so one of the higher people may want to verify.
Also, I’ve seen people using よ even in humble form when speaking with business associates/ customers. So, no, I don’t think it is rude or even really a colloquialism at all.