Why does barbecue sauce break down and become watery in baking
When you bake meat, certain proteins in it change and contract, squeezing out liquid. That liquid will mix with any miscible liquid around it, of course. The result will be colored like your BBQ sauce, but will be diluted.

If you'd like to have a thick glaze of BBQ sauce on the finished meat, the solution is to apply it late in the cooking process, once much of the liquid has already come out of the meat. Once you've added the glaze, make sure not to cover the meat: you want additional water vapor to float away, not to re-condense and rain on your ribs.

Now, if you'd like to improve the flavor and texture further and don't mind spending more time to do it, you can do a hybrid of those two methods. Cook the meat with the BBQ sauce, tightly covered, until almost done. Drain off and reserve the liquid. and skim off as much fat as you can. Boil the liquid down in a saucepan until it's quite thick, then re-spread it on the ribs. That process takes longer, particularly if you're being really careful about the fat, but the gelatin and flavor in the resultant glaze will be worth it.