I doubt AM4 Motherboard will be popular among altcoin miner since the MB and CPU price is higher than intel PC unless they also plan to mine altcoin with CPU.
I think the reason biostar (and all MB manufacture) use word "Bitcoin Mining MB" because bitcoin is popular and easy to remember than cryptocurrency mining MB, altcoin mining MB or ETH mining MB
I agree that the AM4 platform doesn't have a great super-cheap GPU option, but it does depend on how expensive these boards go for. If they are sub $70 you never know.
And I agree as well that if you call a board a "bitcoin" motherboard, everyone will assume 6 PCIE slots.