The biggest obstacle to this is not necessarily technology, but the vastly different ways SaaS companies opt to go to market via reseller channels - or don't. Google and Microsoft have both had established reseller channels for a long time, but there are still major vendors who only recently (or still haven't..) established this.

Slack is a great example - they only sell direct. And companies who use Slack have a tendency to "sprawl" into other SaaS apps that may not have a reseller channel, creating a bit of a snowball effect. Contrast this with companies "bought in" to Microsoft where it's much more common to see them adopt Microsoft Teams and other technologies to avoid that sprawl - and they typically buy via Microsoft partners who can bill them on a single invoice.

While we can't force SaaS vendors to acknowledge that customers want a single bill/distributor, we are working on the problem further upstream by creating a marketplace [1] backed by a network of connectivity agents who are expanding into the SaaS world. One point of purchase/bill for connectivity + SaaS (and IaaS) with additional benefits such as management, etc. Even more interestingly, we're covering the developer, distributor, reseller, and customer channels on a single platform.

[1] https://www.appsmart.com