Well to be clear, the difference between offering Open Source vs proprietary can be significant.

In the Enterprise space, they have the finance, experience (i.e. Management is comfortable with proprietary), and can easily find expertise across all their vendors. So when they need say, a telephony solution for a business unit that is different from the primary Corp solution, they can be confident any vendor will be comfortable working with windows, domains, etc. So it's not just about in-house support capability.

Then there's the whole risk management aspect of enterprise. No manager is going to sign off on the risk of using open source, when a well-known proprietary solution exists, or perhaps there are multiple proprietary solutions to choose from, and since they're all from large vendors they can contractually offload the risk of those systems to the vendor implementing them.

In a nutshell, proprietary provides a predictable cost for performance that they're familiar with. Predictability is practically the primary goal for enterprise IT, even if cost is greater.

When looking at SMB, part of their challenge is similar, in that they're often paying a vendor to manage their systems, and again, the known-quantity of well-established options is hard to overcome. How many SMB vendors have extensive OSS expertise in staff, vs how many are familiar with the mainstays?

If I were managing an SMB support org, no way would I offer OSS - it does nothing to help me reduce risk, minimize hours, etc. It may cost significantly less for my clients, but that's frankly a whole lotta not my problem. From a stability, predictability, support standpoint, mainstay is just easier to support and manage.

Picture a modest SMB support org, with 20 engineers, probably 50 or more clients. You also then need a help desk for those simpler issues that don't require an engineer's time (password resets, software config, etc). So I'm gonna say 10 people on the help desk. Where do you find a large enough pool of talent to interview for help desk that has OSS expertise?

Also, once you're paying for MS licenses, you're sucked in. Again, the devil you know.

I despise SAAS, cloud everything, etc. Google can pound sand, with MS in the front of that line. But they still provide what businesses are looking for, and that's really hard to work against. Not saying we shouldn't keep pushing, just providing a perspective as someone who's worked in both Enterprise and SMB, and I still have friends in both.