" My mortgage is 2% interest. I could pay it off but why"
This isn't "wrong" ; you will find FA's that espouse this theory a lot. I.E you can invest the money that you'd be using to pay down the principal/ pay off the 2% (it's probably actually 3-5% but ok, we get you are embellishing to try to make your point)---ANYWAY, theory being you're going to make a lot more money investing that money you'd use to pay down /off the mortgage. So keep paying your mortgage and invest.
At some level makes mathematical sense, but the factor left out of the equation is RISK. The very real risk that you will suddenly be without that income for a while (read: Layoff) . Would you rather be laid off for a while without a mortgage, or with one? And sure, if you have your i's dotted and t's crossed, you'd have a good emergency fund to carry you through that period. But I'd be willing to bet most won't.
If you want to prepare yourself, the smart thing to do if you're able, is to pay off ALL debt, car loans, mortgage, etc. Then save that 6 months of expenses emergency fund. And hopefully you're still here and after that you can invest like crazy.