Why not? You don't have to use them if you don't want. There is many apps that you can't get on UT and most likely now that Canonical ditched the project even more so.
Whatsapp is one such case and sadly it is so widely used that it is impoosible to sell people alternatives. Spotify might be next one. I also have few work apps that i need and must use Android phone @ work. Otherwise i would use my dualsim Pro5.