Sorry that isn't how the law works. Unless those people travel out of the country to conduct their work, they're breaking Thai law - it doesn't matter where the company is, what matters is that they're doing work in Thailand.
By your logic, it is legal to drive over the posted speed limit in Australia.
Thailand is notorious for how it's laws are enforced. Earlier today I had to stop and wait (on foot) in a traffic lane, because a motor scooter was driving the wrong way in the parking lane past a police officer, who did nothing.
Just because the immigration chief in Chiang Mai over 3 years ago said remote work is ok, doesn't mean it will always be this way.
You are at the mercy of the officer in front of you.
The counterfactual would be that if this were possible, every foreigner in Thailand would be made an employee of a company in Ireland or something to avoid dealing with visa issues (or tax issues )
In reality, it's a non-issue for the reasons above.
https://ashleyconnor.co.uk/2014/09/07/the-digital-nomad-and-...
You can't really work anywhere in South East Asia without a work permit. Cambodia used to be the easiest place but last time I looked they were changing the law.
A lot of these laws were made before remote work was even a thing.
Some countries do allow remote work. Canada being one of them.