Ask HN: Why isn't there a Saas-for-Saas?

I know this question has come up at least once in the past (can't find it now), but afaik without a clear answer.

So let me ask again: why isn't there a Saas-for-saas that takes away most of the common technical chores for getting a Saas in the air, and instead allows you to focus on getting your Saas-specific code out?

Setting up a Saas and getting it out there as a MVP, not to even mention a production ready version, requires a lot of similar effort between Saas'. I.e.:

- user/tenant management. Oauth + email/password, 2-factor, mail/sms flows for reset, etc. - plan/package management + RBAC / access control + rate limiting and/or overcharges on pay-per-use basis - connection to payment provider(s). Say Stripe + Paypal for pretty good coverage. Needs to cover correct VAT handling - exposed self-service userprofile / saas-preferences / payment options / billing statements / 'currently accrued this month' statement, etc. - might be API only. Community will take it from there with canned Gui templates using bootstrap, etc. - ...

Auth0 for instance tackles the user-management space pretty nicely, and it might make sense for this Saas-for-Saas to optionally outsource that part to them for all the extra stuff they provide (LDAP, etc). However, just as an example using multiple users under 1 tenant-account is not straightforward.

So why is it that such a Saas-for-Saas doesn't exist? Do startups hesitate to outsource this core-functionality? Do they just wing it, and later pull their hair out when realising that doing it properly takes far more time than anticipated? Or is selling to the startup-crowd just really tough?

Lastly to note: It doesn't have to be a Saas per-se. Could just as well be open-source code with a commercial license or something. It would have to run entirely separate from my own saas-code, but that's perfectly doable. I'd pay could money for this.

Anyone?