The key thing to remember is that, pre-multimedia/pre-Internet, Canada had effective government control over broadcast media. Actually, every country did, because broadcast frequencies being finite was an effective counterargument against the 1st Amendment. Canada in particular used their de-facto censorship power to enforce "Canadian Content" regulations - as in, your radio station must push a certain percentage of music or talk shows deemed sufficiently "Canadian" enough by Canada's radio regulator.
The Internet functionally destroyed this regime by walking away from publicly regulated spectrum. Canada wants those powers back, so they passed a bill which lets them apply Canadian Content regulations to streaming services that Canadians use. The podcast registration requirement is an extension of this: if they plan to require that people listen to[0] a certain percentage of Canadian Content[1] podcasts, then they need the services that push them to users to register so they know who to enforce the rules on.
Website hosts and stores would be regulated under other rules that are very similar to the ones in other Anglosphere countries, i.e. without this weird censorship regime. It's only "streaming services" - i.e. "websites that look like something that would have been regulated under CRTC CanCon rules if they didn't have the Internet" - that are getting regulated here.
[0] The Internet is ostensibly a "pull" medium, but in practice, everyone has recommendation algorithms which look like a more elaborate version of a broadcaster if you squint at them.
[0] Which, BTW, is not content made by Canadians. If you're a Canadian creative you have to jump through a lot of hoops in order to be officially recognized as "Canadian Content".