I'm not a professional about XPEnology but here is some thoughts about this:
On one hand, the OS from Synology is not designed for supporting all the hardware existing on the market. I think that synos are based on few different hardware configurations. So in order to be able to support all our hardware configurations many hardware drivers need to be added.
On the other hand, perhaps there are some new security features added by Synology to avoid this new 5.x to be used on other config than their own.
And a lot of other things to do, fix or adapt!