Why does Google Tag Manager use iframe and not the script dom element?

@arlo 

Google Tag Manager (GTM) uses an iframe to load and execute tags on a website for a couple of reasons:

1. Security: By using an iframe, GTM can isolate its scripts from the website's scripts and content. This isolation helps prevent conflicts with the website's code, which could potentially cause errors or security vulnerabilities. It also helps protect the website and its users from any malicious code that could be included in the tags.
2. Simplicity: Using an iframe simplifies the implementation process for GTM. With an iframe, the website only needs to include a small amount of code to load the GTM container. The container then takes care of loading and executing any tags that are configured within it.
3. Cross-domain tracking: If a website wants to track user behavior across multiple domains, it can use GTM's Cross-Domain Tracking feature. This feature uses an iframe to pass information between domains, allowing GTM to track user behavior across multiple sites.

While it's possible to use the script DOM element to load GTM, doing so would require more complex implementation and could potentially introduce security risks. The iframe approach used by GTM helps ensure a simpler and more secure implementation for tracking and managing tags on a website.