> Yes, they entered the market around those years, but what does that change?

It means the hardware was purchased after it started to be discontinued.

It's hardly a reasonable take, and makes little sense, to complain how you can't upgrade hardware that was already being discontinued before you bought it.

> DDR3 and LGA1150 were not deemed "legacy" the day DDR4 and LGA1151 motherboards entered the market.

I googled for LGA1150 before I posted the message, and one of the first search results is a post on Linux tech tips dating way back to 2015 on whether LGA1150 was already dead.

And you purchased the Mobo one year after that.