The ICANN vetting process and procedures to set up a new gTLD (let's use .network as an example) are much more thorough than the traditional two letter ccTLD. There are ccTLDs run by countries that edit the zonefiles by hand and don't even have a WHOIS server online.
for example using the current issue, nic.sm doesn't even run https on their webserver.
Or if I buy a .com from namecheap I can set up 2FA at my registrar, point it at my own authoritative nameservers, and trust that it won't fail.
If a SaaS doesn't pay their AWS bills, they get turned off, it's not on AWS to keep the SaaS' customers running, and if AWS doesn't pay their electricity bill - - etc.
There are some registries which don't have registrars, and in that case "suspend the registrant's domain name until paid" would be a reasonable expectation, but it's definitely the expectation of most registrants that their registrar isn't providing availability-critical service, merely facilitating updates. (Unless the registrar is also providing DNS hosting, which is generally a bad idea IMO.)