Part of the purpose of a CRM is not just storing contact records (that's the most bare-bones use-case of a CRM) but rather to be a central hub of communication across your company.
You email a customer and someone else on your team emails that same customer, how do you know this happened? You don't when using Google Sheets as a CRM. So customers may get 2-3 emails from different team members and it's a mess.
A proper CRM is going to ingest emails automatically, count the number of interactions you've had with someone, and nudge you when you're not doing a good job at staying on top of leads. Your Google Sheets "CRM" on the other hand will not be able to handle this type of communication tracking.
In addition, tracking who opened or clicked your emails is helpful information that can help close a sale.
A CRM can roll up these actions into a score, so your team can easily identify engaged leads. A good CRM will also mention the last date of a specific interaction, or how long it's been between interactions so you know it's time to follow up.
Also trying to manually update Google Sheets every time you've had an interaction (like an email) is time-consuming and will quickly become a burden to your team.
Sheets is flexible enough to begin looking like a CRM, but is missing the actual capabilities that make a CRM work


