The anti-monopoly benefits of interoperability can be offset by the regulatory capture of forced interoperability if companies too small are subject to such rules, placing them at a disadvantage relative to largest players and increasing the likelihood that the status quo remains in place. That's the "Can't have your cake and eat it too" that's being referred to above I think—in other words, if you regulate the second-tier like the first-tier, the second-tier will never have a chance at becoming the first tier.
Slightly off topic, but you managed to clearly articulate what bothers me about a lot of well meaning regulation. GDPR in particular comes to mind - I was never worried about what some small time blogger was doing with my personal info, only (for example) Google and PayPal.