Would anyone store banking credentials on google drive ? I guess no. The same goes with bitcoin private keys.
In fact, it would be best to keep the private key as offline as possible. No google drive or any kind of cloud storage.
There are merely people who do this risky backup method but it's untrue to say nobody do this.
Sometimes, you will see people reported their losses of bitcoin and cryptocurrencies by poor backup methods and this method is possible one for those inexperienced and careless people.
If they know about good recommended backup methods, and they are carefull with backup practice, they won't do this, but firstly they need to be well educated about wallet backup as well as risk of online storage.
How to back up a seed phrase?