A lot of things are due to politics involves government income.
You forgot what really happen to one of our previous Minister of Communications.
Basically if you did too good of a job, shareholder is not happy. Check out who is TM's majority shareholder.

To me the most effective method is allow multiple last-mile provider. The advertisement and competition will take care of things.

BUT this is also the reason why they do not want multiple telco to build out 5G network. The government want to be in a position to do price-fixing. For U, they quickly announced all fiber will be provided by TM, same goes for DNB.

Same story with submarine cable landing station. You need cable kuat to even build one. Look at who owns all the cable landing station in Malaysia.

Like blacktubi said, this kind of thing is not exclusive to Malaysia.
In China the big 3 state-owned telcos control 95% of the user base. They practice a lot of gatekeeping.
Chaebol controlled telcos in South Korea did the same.
NTT in Japan.
TATA in India.
NBN in Australia.
Sprint, Lumen, ATT in US.