MS is not a monopoly there, and always have been, alternatives available. MS have a huge market share simply because the average user and corporate buyer has an IQ that score with a single digit, and a value below 5 (or they appear to have).
MS design software for easy use by non-technical people, ie 95% of the population; the fact that it also suits morons is a side issue. They design to the minimum standard for the majority of the market, and are bloody good at doing that.
When MS entered the market the majority of software was designed for research labs and tested to a fare-the-well, thus they were priced at a few thousand dollars each (comparable to paying about $20,000 today). MS marketed an inferior products that met minimum user needs for a hundred dollars or so. This made the software cheap enough for anyone to buy and coincided with IBM clone computers being available for a few thousand bucks instead of tens of thousands.
Most MS software was capable of being installed and set up for basic use by almost anyonbe, all the available opposition required a highly trained tech to install and set up. The wonder is not that MS got such a large share of the market, the wonder is that anyone elese retained any market share at all.
Since then people have stayed with MS on the basis of 'the devil you know', or too lazy to learn how to use anything else. As a result anyone wanting to lure average MS clients away from MS have had to mimic MS operations so that the users don't have to learn anything new.
Good points for MS have been dramatic reduction in software prices (here we are over 20 years later and they have not yet returned to the pre MS dollar prices despite inflation etc), easier user usability, general use of computers.
Bad points for MS are that it is still chintzy software, aggressive sales techniques (learnt from IBM, Prime, Apple, etc), a company setting some industry standards.
Personally I expect that MS will soon change some of their directions or start to see major changes in their market share.