120hz at 5k requires Thunderbolt 5 (ie better graphics card, more info down the pipeline.
Which is why most of the PC world is on cheap 4k monitors still.
According to the Steam Hardware Survey for last month, 47.91% of Steam users are on 1920x1080; adding the 2.56% on 1920x1200 means that a majority of users are still on 2K. The next biggest chunk of users are on 2560x{1440, 1600}, at about 32%. Only 5% of users are on 4K resolutions or greater.
And these are gamers, who are more likely than the average user to care about graphical fidelity. Most of the PC world just does not care about 4K, period.
Most 5K monitors on the PC side are not going to be driven over Thunderbolt, but rather DisplayPort or HDMI.
And the most popular resolution on PC is not 4k, but rather 1080p and 1440p.
Because that market, in aggregate, only spends extra on monitors for gaming.