This is how it's always been. You just noticed.
More models have been splitstreaming because technology has made it easier to do so. Back in the day, you would need multiple computers because CPUs couldn't handle it. There are now programs out there where you can condense all your sites into one chat, so you aren't using multiple desktops or constantly swapping between tabs.
I get it may be annoying if you don't have her full attention while she is live, but she is trying to make a living. Pay her bills, save money for the future, support her family, whatever. Sometimes one camsite can't cut it, so models HAVE to do multiple sites. So if you want a model's attention, you need to pay up. if not, she is going to focus on her other site where someone else is paying more. Even if you are tipping, but if the model has an opportunity to make MORE, she is gonna take it.
I think a lot of you dudes forget this is work.