A few reasons:

• Any conversion (including internally at the display) can result in colorspace mismatches.
• If the sink has an unsupported mode, the source will send a default - which is usually a mismatch.

I wouldn't call it often wrong, personally. I'd say some devices are really bad with EDIDs, and are consistently problematic. It's more like -recent hardware is generally pretty good, but relying entirely on EDID won't always work, so use with care.

Some great examples of problematic devices/situations (in general):

• Apple. Pretty much anything they make.
• DP to HDMI - while DP supports HDMI natively, that can be one of the situations where EDID issues crop up. But much less often than....
• DVI to HDMI or vice versa - this is probably the most problematic of general use. Happens somewhat often where a different or default colorspace gets used.

If you've got a single PC going to a display (or several), just set it once manually and you're good to go. If you're plugging and unplugging often with multiple devices (like with a dock), an EDID minder can be handy, but come with a price that generally makes setting it manually preferred anyway.

Hope this helps answer for you