1. It's going to be very unpopular, enabling the domestic opposition to take advantage rhetorically. Without a local mandate it's political suicide, so you'd need to build up to it for a while and turn the public against Facebook/Instagram. Tricky if that's their primary mode of engagement with community/news/entertainment.

2. An attack on a powerful private company tends to scare other capital owners. If you depend on donors and local (or international) businesses to maintain your lifestyle or electoral viability then it can be tricky to convince them that your ban is limited in scope and won't prompt additional regulatory action or contribute to a social shift of people expecting more from their leaders. If you fail to provide adequate assurances then capital is likely to side with Meta and sink you for trying to cut them off.

Also, if you help a dictator-wanna-be to take power you may get a election short-term but a country long-term. Billionaires are not very friendly towards democracy or the working class.