Actually, I was just wondering in my mind that what could have caused the downfall of all these Telecom company and why they just went down the drain like that?

I am only familiar with Starcomms and Ntel.
It was poor planning.

The Starcomms example happened to a lot of their predecessors: they create the network, it’s fast as Bleep, they sign up people who enjoy the service for six straight months.
As time goes they start adding more customers than necessary to the overburdened network, they make a lot of profit and eventually the network crashes and the company packs up shop — making tenfold their original capital.

The ordeal over the years gifted me tens of useless modems from different ISPs.
I now stick to MTN alone to avoid a repeat of such.

As for Ntel add an ‘i’ to make N[i]tel.
Are things clearer now?

I remember using Visafone back in the day so I believe they followed the same route.
Their 4G service was really fast, though.