Because many jurisdictions have regulations that target large corporations and large is objectively defined in the rules as some number of users. (I am using large loosely. EU defines very large as 10% of the 450M EU consumers).

EU statute has both monthly reporting, yearly and 3 year trends for determining specific applicable rules for large operators.

Example:

The regulation that Apple is trying to comply with EU Digital Services Act [1], [2]

The EU Digital Markets Act [2], [3]

(India) Information Technology (Intermediary Guidelines and Digital Media Ethics Code) Rules, 2021 (updated 06.04.2023) [4]

(Germany) Network Enforcement Act [5]

(France) Law requiring large social media operators to remove hate speech, crimes against humanity, sexual harassment etc., [6]

[1]: https://digital-strategy.ec.europa.eu/en/policies/digital-se...

[2]: https://commission.europa.eu/strategy-and-policy/priorities-...

[3]: https://ec.europa.eu/commission/presscorner/detail/en/ip_22_...

[4]: https://www.meity.gov.in/writereaddata/files/Information%20T...

[5]: https://germanlawarchive.iuscomp.org/?p=1245

[6]: https://www.assemblee-nationale.fr/dyn/actualites-accueil-hu...