> Care to expand?
Certainly. It's not access to free OSes that's the problem - it's that both the major one and most of the minor ones are derivatives of either UNIX or the POSIX specification. (Haiku is the only semi-popular one which attempts to do something different.) There's little chance of stepping outside that box in any major way.
For example, a slowly-moving research project of mine is to build a fully functional OS that uses capabilities, per-application sandboxing, a generic object store instead of a filesystem, a built-in intra- and inter-computer RPC mechanism, standardised configuration (from the network admin level downwards), and a powerful Smalltalk-based GUI for managing all of this, on the idea that today's information workers need better ability to manage and script their system, including building new applications out of existing ones. The Linux ecosystem doesn't provide a meaningful, standardised interface for doing so for many office-y applications or complex formats.
While you could theoretically layer all this on top of POSIX (and in fact, that's the first implementation of my system), you are at the same time throwing away 99% of POSIX, and you are highly expected to maintain compatibility with apps for the system you're building on top of - which likely don't fit in with your system's design, and doesn't encourage the creation of applications for, or modification of existing applications to fit, your new system design.
This sort of greenfield R&D is what's been missing. Even universities are primarily stuck getting POSIX running on various kernel architectures, avoiding the topic of OS design entirely. You could point towards Android as a counter-example, but that's not a desktop OS - its primary competitors were proprietary OSes made by the smartphone vendors, and it's still not really capable of being used as a primary OS.