That's not the point here. It's an adversary getting two CDNs to loop eachother and launching an attack that way.
If CDN A proxies requests to CDN B and CDN B proxies requests to CDN A then those two will DoS eachother fairly quickly.
There is no attacker inbetween to strip the Via, that would be counterproductive to the attack.
Email has this too; the Received: header. If you manage to get a loop between two MTAs going they will detect it by seeing themselves in the Received: header list.
If CDN A proxies requests to CDN B and CDN B proxies requests to CDN A then those two will DoS eachother fairly quickly.
There is no attacker inbetween to strip the Via, that would be counterproductive to the attack.
Email has this too; the Received: header. If you manage to get a loop between two MTAs going they will detect it by seeing themselves in the Received: header list.