Why? It seems like “gonna” has entered the lexicon as an alternative to “going to”, languages change over time. Are you mad people say “hi” instead of “hello” as well?

In particular, the Harris campaign’s biggest strategy is staying energized and getting younger people to actually vote. The way you keep younger people engaged is to use language familiar to them. Talking like a stuffy politician isn’t motivating to apathetic voters tired of stuffy political rhetoric.