They are not true monopolies... but they are used on a name basis. For example, what FB gives, and only FB does is the fact that it has a lot of momentum behind it, and people tend to use it as a primary way of communicating.
In the past, I was shown the door during job interviews because I didn't have a FB or Twitter account, being called a "fossil" since I didn't spew my life's trivia online for all to read. These days, my Twitter account is a placeholder with some sterile, sanitized stuff on it, and FB was that way for a while until people decided to move all their private forums to FB groups.
So, yes, there are alternatives, but using them is like going to the sports bar that has 1-2 people in it, when everyone else is hanging out at the chic new night club downtown.
As for regulations, this concerns me. Smartly done, it would be a good thing, especially with data privacy and retention items. However, realistically, I fear that regulations would do far more harm than good, and what happens is that they get danced around (or just ignored), and the end subscribers wind up dealing with it. For example, if every country followed Russia's lead and demanded their data be stored on servers at their borders, this would allow domestic spying to easily find would-be dissidents and political rivals would get the Nemtsov treatment a lot quicker in some nations.
It would be nice to see items like the right to be forgotten and a default data sunset life (where if the user doesn't explicitly state the data is permanent, it gets erased after 1-2 years), but here in the US, I rarely see regulations benefiting the end users as a whole. For example, when the EPA tightened the noose with no real warning on the steel industry, the entire sector wound up bankrupt since they couldn't compete with Chinese firms that didn't have to deal with all the Draconian regulations, especially with no protective tariffs to level the playing field.