IP reputation/blocking. Often datacenters have a bad IP reputation and if you access a site with a captcha from a datacenter IP, you will often get more/harder/slower captchas to solve. Some IPs are completely restricted from accessing sites which have captchas, if they are known to be used for spamming.

Embedded references to external javascript libraries, fonts, images, and so on on a web page are resolved by the browser by making a connection to the service that hosts the resource, and connections over the Internet necessarily involve two IP addresses of some sort, the IP address of the requester (or a requester) and the IP address of the responder. Every web browser works that way by default.

There are two basic choices to avoid that - in some cases you can just host the resources yourself so the client browser does not connect to hosts operated by others, or you can operate a proxy so that the client browsers requests are relayed and anonymized before going to a third party.