What are the effects of very few "big tech" companies having a monopoly on how people get information, shop, and communicate?  ?

They don't.

Just because a company dominates the field doesn't make it a monopoly.

Take Amazon. 

You know why they aren't a monopoly? That is because anyone can set up their own website and sell directly to consumers.  Amazon just dominates the field.

Same goes for Google.  Plenty of other search engines out there, they're just not as good, so fewer people choose to use them.  Still plenty of other ways to advertise your goods for sale, but they're not as easy or as well run.

Don't like Facebook?  Then don't use facebook, but don't mewl on about how facebook is so popular you can't get anyone to join crank.net with you.

There are monopolies, but none of the things you mention are monopolies.

Those "big tech" guys don't play Monopoly.

It has cost many people their lives.