Trump's use of vernacular and directness is not a sign of declining cultural standards: it's a calculated rejection of the political class.
The "articulacy" and "civility" of language from establishment politicians has always been a virtue signal, and it's much more so now than it has ever been before. The liberal elite have spent decades developing their own language, one which they use to communicate with each other and to signal their allegiance to that ideology. The use of indirect, noncommittal descriptors, the constant buzzwords, the veneer of civility barely covering up a sneering sense of superiority: all of these things are the hallmarks of the new chattering class of midwits, who are very well-educated, but not especially intelligent and utterly incapable of thinking outside of their own dogmatic box.
Their language is the language in which they communicate with each other, and over the heads of the voting public they hold in such contempt. Its every syllable is a flex: even when they deign to talk to you, the language they use is intended to make it clear that they're talking down. People got sick of it, which is part of the reason Trump has been so successful. He doesn't talk down to you: he just talks to you. He's direct, he uses simple language and he's not afraid to call a spade a spade. It's very deliberate, and people find it refreshing.
I've spent enough time around the political class to know that the language you hear them use in press conferences, debates and interviews is not reflective of the language they used in their own circles. No one swears as often or as creatively as politicians and civil servants when they don't think there are mics around, yet in public they all resort to the same coded platitudes and buzzwords: a language designed to appeal to the sensibilities of the "educated" class, because those are the people whose approval they yearn for. But Trump uses the same language in public that he uses in private. It's one of the many things that makes him so appealing to ordinary people, because it signals that their approval is what matters to him.