It's called "lock-in". First give users the service for free, then limit where they can use it and move some features to the subscription only area. When users have reached a certain amount of people. BOOM! Forced subscription or forced usage of a certain proprietary software (Chrome) to use the service.
The same thing is happening to Windows 10.
Fun fact: Google is stealing your data if you use Chrome via many ways. Among them is a software called software_reporter_tool that scans your hard drive and other stuff.
Here's another example:
You can find it here: chrome://settings/searchEngines?search=search
This is the default search engine:
"{google:baseURL}search?q=%s&{google:RLZ}{google:originalQueryForSuggestion}{google:assistedQueryStats}{google:searchFieldtrialParameter}{google:iOSSearchLanguage}{google:searchClient}{google:sourceId}{google:contextualSearchVersion}ie={inputEncoding}"
This is what google actually need to make a search:
"https://www.google.com/search?q=%s"
Notice the difference? Google is abusing its position as usual.
People want sync to function since they have a google account but they don't want the privacy and security violations that come with using Chrome.
I'm hoping EU will step in soon. It's monopoly behavior to remove sync from Chromium. It's free after all so what is google butthurt about? Oh right, they can't track and collect user data since that's the first thing devs remove in their Chromium fork.