The cynical side of me is saying the following:
1) Taylor Swift has enough money now that she feels safe in speaking her mind even if it's going to damage her brand and image among her fanbase
Or
2) Taylor Swift has canvased her fanbase enough to know that Trump/Republicans are sufficiently unpopular among them to chose now as the time to "go political" with minimal impact on her future earning potential.
Everything I've read about Ms. Swift (which is not much) is that she is a shrewd business person who understands that her brand is build on her public image, and so does everything in her power to keep that public image clean and universally approachable.