Ported means you need the developers to want to do it. Many do not, or they make lesser versions for iPads. iPads running Mac apps natively eliminates that problem.
If a MacBook Air can run it, an iPad would be able to.
As someone who leads operations for a 200+ person development company, consults with client decision makers and product owners on solution strategy / requirements / design and personally develops apps and writes code, my experience and observation is that no one approaches iPad development from the perspective of “let’s port an existing app exactly as-is to iPad.” The considerations and priorities are consistently:
1. Functionality - Identify the Pareto Subset (the proverbial 20% of functionality that delivers 80% of app utility)
2. Design - Simplify presentation and workflow (less is more)
3. UX - Make it intuitive by adapting app to deliver #1 and #2 in alignment with device/OS conventions
The net result is that a well defined iPad app is intentionally simpler than its corresponding desktop app — not because of iPadOS or Apple-imposed restrictions but because of product owner / developer choices to improve the product.
Now obviously there are some constraints that add development friction (e.g., device hardware and information access), but these are due to device and information security considerations, and the APIs are consistently evolving to expand and simplify secure developer access to these resources — not to lock things down as is implied in a number of comments.
Making macOS available on iPad would not be the panacea that it appears to be. That’s because doing so will allow wholesale circumvention of this app adaptation process and result in compromised UX — because the iPad is not simply a display. It is a system that is built from the ground up to support tablet operation with specialized hardware, firmware and software and thousands of optimizations across the stack. Simply porting macOS is the equivalent of a hack job and the results will show that.
If you really want to understand the reality and facts of iPadOS development just download the Apple Developer App and explore the thousands of videos and other resources that Apple invests in creating to assist developers. An honest assessment will reveal that app development is gated by app complexity and developer skills and effort — not Apple or iPadOS restrictions.