the four listed are the biggest products in the world in their space. the first three would be multi billion dollar companies outside of Google.
not to mention Search itself, Docs has become a fantastic product as has Photos. of course they have killed hundreds of potentially great projects (RIP Reader) but give the company their due - they know how to build products.
>the first three would be multi billion dollar companies outside of Google
Gmail got popular because it's free (and had large space for a free client). If it wasn't to be outside of Google, it would make an insignificant amount of money through ads, or started to charge (in which case users would flee).
Ditto for Chrome. There are 4-5 free browsers, nobody would use a browser that's not free (a required for it to be a multi-billion dollar company). At best they'd sell their search bar default setting, like FF does, which is less than a billion IIRC.
Gmail would not be a multi-billion dollar company. It doesn't make money (remember they don't target ads on email content anymore). You'd have to roll in Google apps for business to get to the money making part.
Chrome definitely isn't a multi-billion dollar company. There is no revenue stream there. Firefox only exists by selling the search bar and being a non-profit.
"the first three would be multi billion dollar companies
outside of Google"
I think this is the problem. Google does not care about products smaller than that. They will happily shut down a product because it's too small, even though it would be a reasonably successful business on its own.
However, "reasonably successful" is not good enough for them.
Google has killed off dozens upon dozens more officially launched projects.