Small matter of a global financial crisis the likes of which hasn't been seen since the 1930's between the campaign and his coming into office may have had something to do with that.
Sure, but Obama was President for 8 years. There was a crisis, but the common view is it lasted at most 2-3 years. That saving operation was meant to be a short term fix, with low interest rates to save the banks. Between 2008 and 2015, interest rates were at zero. Under Obama nothing changed, except for his last year.
I believe Trump had a point when he said the economy was a bubble. Keeping interest rates so low for so long was a mistake. The problem is Trump now says we have a booming economy (of course because of him), but he now wants to use the same concept that was used during the crisis. That sums him up. There is no logic, just statements.
It's a topic for a different thread perhaps, but I believe the current low interest policy, used by the European Central Bank to a larger extent than in the US, must be completely wrong. Basically it's a policy that punishes savers. Trump wants to have the same in the US. The effect is that the stock market and for example real estate will get more expensive. And that's probably the reason he wants it.