Why do some CS2 matches have no player props at all (only match winner / map winner)?

The match does not meet our internal rule for publishing player markets. Player props require the match to satisfy the tier + data-coverage threshold. As a general guide for clients: if you can see essentially all the side markets for a match, you can expect player props too. If a match is missing most side markets, player props are unlikely to be available.
<span color="red">Internal information</span>: The rule is OTS8 or higher + HLTV + DATA. I would recommend to say they can expect player markets if they see pretty much all the sidemarkets.