Android is open source, at least the core android is.
However, the whole ecosystem is still closed by Google. The hardware isn’t open either, and if you just want to use “stock” Android devices that you can buy, then a lot of the built-in Apps require a Google account.
Not everything has to be free or open source, so if you want to buy or sell Android apps, your only real choice is Google Play. If you want to buy Google devices like the Nexus, you also have to use Google Play. And your only payment method? Google Wallet. (Which only supports credit cards as payment)
So what happens if Google closes down your account and warns you in bold letters to not try and open a new one? You’re on your own. Submit all the identity documents they request, like passport and utility bill? No response. Write an email to any of their support addresses? No response. Fill out dozens of web contact forms in their help? No response. Call them after you have found a US phone number only visible when the help language is set to US? “We apologize for any inconvenience…”
Want to give your hard-earned money to google for one of their devices but they don’t want it? Running after them trying to get your account unlocked? How silly is this.
Maybe it is comforting then that you are not alone