If a malicious actor gains access to your Google, Apple or Microsoft account, they could also gain access to your synced 2FA codes. This completely defeats the purpose of 2FA as it would allow the malicious actor to reset passwords and sign into any account you use with your Authenticator App.
Additionally, every device with access to your cloud account becomes a potential entry point for malicious actors. More devices = more risk. Due to this security risk, Kraken recommends that you disable Google authenticator cloud sync.