Some would argue making payments even more seamless online is a bad thing because it's just so easy to buy all the things. But having to login to a payment service every time you click the purchase button is a hassle, so PayPal is making it easier for anyone who has a Google account.
PayPal already enjoys a relationship with Google, allowing users to pay using their PayPal account through Google Pay in stores, in apps, and online. But that partnership is now being extended to cover the entire Google ecosystem for anyone in the US.
Once PayPal has been added to any one of Google's services through your account, it will be available as a payment method across all Google services you have access to. So if you add it through Google Play, for example, PayPal will be available in Gmail, YouTube, on the Google Store, and anywhere else Google has a presence. Additionally, there's no extra login required because that step is removed as soon as you link up the two accounts.
PayPal is clearly hoping this will boost the number of transactions carried out each day through its service, and therefore the revenue it earns every time a payment is made. And it seems likely that will happen due to how convenient linking these two account will be for many Google account holders.
Google also benefits because the integration means you no longer need to leave one of its sites to go and pay for something as it's all done right there on the same page with the click of a button.