Does it need to be? x86 had every opportunity to become a locked-down, exclusive standard too, and it grew the way it did, into a cross-vendor standard, for a reason. Why will a similar trajectory not apply to the M1?
The history of the x86 instruction set is very complicated and involves a number of lawsuits and settlements. What you see today is the fruit decades of fighting and wrangling.
As far as I understand, x86 is a duopoly, and AMD is allowed to produce it because antitrust litigation resulted in Intel being required to allow a second party to implement their instruction set.
Also Intel is a very different entity than Apple. They produce commodity hardware, where Apple creates consumer experiences. Apple's incentive is to keep M1 closed to give their software ecosystem an edge vs. competitors.
Does it need to be? x86 had every opportunity to become a locked-down, exclusive standard too, and it grew the way it did, into a cross-vendor standard, for a reason. Why will a similar trajectory not apply to the M1?