The only reasons I've heard as to why we are currently in a housing bubble are that prices have gone up significantly in a relatively short period of time and because housing prices are higher now, adjusted for inflation, than they were before the GFC.
However, I've heard far more reasons, which I also find more compelling, as to why we are
not currently in a housing bubble. Those include the facts that it's much harder to get a mortgage these days and those mortgages are generally not for 100% or more of the value of the property, the price of new construction being much higher now than ~14 years ago, there not being enough housing for everyone who wants it, and interest rates being significantly lower now than before.
For those who think we're in a bubble already, what's going to 'pop' it? Interest rates are very unlikely to suddenly spike, people aren't likely at all to suddenly default
en masse (the
delinquency rate on SFH mortgages didn't even hit 3% in 2020 and has remained lower than where it was for all of 2018), and demand for housing isn't likely at all to suddenly drop.