Because you didn't buy it from Visible! Visible has put all android phones on the blacklist that they have not sold in the current year. With the new plans and the new system rolling out phones that are compatible on the old plan may or may not be compatible with the new plan. I bought a phone from here last year and it currently work with the old plan still but says it is not compatible with the new plan. It is sad that Visible is adding to the electronics waste by doing this. Even though they told me they are working on adding as many phones from the old list as fast as possible I just don't think they are working that hard though. Visible is changing to same system Verizon(who owns Visible) is using now they just aren't taking the initiative to fix the compatible issues. Funny my phone is compatible with Verizon but not on the new plan here.
It also may be locked since you just bought it. But, I have also saw unlocked phone from other carriers from eBay that are unlocked that are not compatible also.
I think they honestly don't want people to become customers. That's the only thing I can think of, I just bought a Moto g power from Best buy that came with a month of free visible service and a SIM card I went to activate it and it told me the phone isn't compatible, why the heck would you bundle it together and sell it then? Now I'm screwed because my service ends today through mint and I can't get my device to work with visible.