4 weeks ago
It's hardware, DP 1.4 and DP 2.1 have completely different bandwidth capabilities. Although, DisplayPort 2.1 at present is just about removing DSC which you wouldn't notice if it was on or off anyway (I'm serious, it's imperceivable).
For now it's really just a marketing gimmick, but will be a thing one day when resolutions and refresh rates are considerably higher than they are today ie;- 8k 240Hz. Also there are a few variants of DP 2.1 that all have different bandwidth capabilities, the only one you'd want is UHBR20. And lets be honest, it'll be sometime before hardware will ever be able to drive 8K 240Hz.
3 weeks ago
It's not just about bandwidth, DP2.1 also offers daisy-chaining capabilities. But indeed, it's hardware-limited. No firmware update will get you your DP2.1 capabilities if the HW is only 1.4-capable.