my understanding is for things like eCall that the phone only gets activated when it's actually needed (i.e: an emergency), but never found a check/analysis of this on cars (though i only looked for 2 mins when i checked)

Not yet. But soon, when cars are required to transmit data about emissions.

Which directive is that, and what's the point of it vs emissions point monitoring at annual inspection time?

2024/1257 [0], for checking fleet compliance, not the individual vehicle, anonymously. How a car is supposed to connect to a cell tower anonymously isn't explained though.

"6. The OBM systems installed by the manufacturer in the vehicles shall be capable of: [...] (b) communicating data on exhaust emission performance and battery durability data of the vehicle via the OBD port, including for the purpose of roadworthiness tests in accordance with Directive 2014/45/EU and technical roadside inspections in accordance with Directive 2014/47/EU, and anonymously over the air for the purpose of monitoring compliance of vehicle types;"

[0] https://eur-lex.europa.eu/legal-content/EN/TXT/PDF/?uri=CELE...