I don’t want to assume the Portuguese are quite so Machiavellian. But in addition to what you said,
(1) Portugal already pulled the NHR rug, and many people will be unnecessarily volunteering themselves as tax residents in 2023 & 2024, in order to hold on to the NHR status for the next 10 years.
(2) They only need to close the 7-day-per-year naturalisation loophole by passing laws, issuing regulations, or simply change the interpretation of laws/regulations at AIMA when one applies for citizenship by naturalisation. For example, they can require one to live in Portugal for at least 183 days or 270 days per year for at least 5 consecutive years, in order to naturalise. Then all the GV holders would have to (a) physically move & pay PT taxes in order to naturalise, or (b) pay AIMA ~12.5k EUR every 5 years to keep renewing the very expensive PR GV, or ~5k EUR every 2 years to keep renewing the equally expensive GV.
(3) Under political pressures (long lines at the public hospitals, teachers on strike), they can also pass new laws to restrict new immigrants’ access to cheap public healthcare and education.
Since they are not really worried about attracting new GV investors anymore, they don’t have to care if existing GV investors are unhappy that things we ASSUMED are no longer there.
For people already with a decent passport (that gets 90-day visa free travel to the Schengen area), it makes much more sense to just wait until retirement (or whenever ready to move) and get the retiree/passive income visa instead. Portugal+Italy+Greece+Spain and France and even Ireland will likely always have some sort of retiree/passive income visa around. These are a lot cheaper and get you inside the country in less than 6 months most of the time.