For one, MT4 makes it easier for brokers to manipulate price feeds to their advantage.
Go to top of this page and click on "Education & Forums".....select "Forex Community Forums"....and look for various threads on MT4 platforms............e.g MT4 Brokers side manipulation video started by mamma 04-12-2012, How brokers manipulate prices using mt4 started by chaosscrem 03-06-2012, and many more on the subject.
Bad brokers like it since they can abuse it to cheat.
Good brokers like it since so many clients demand it.
Why do clients demand it? Several reasons. One - Because so many brokers offer it (yes, that's circular, but it's a feedback loop). Two - because there are some many free and commercial add ons. Three - because if you ask a question about a platform only offered by one broker, only that broker or their clients can asnwer it. If you ask a question about MetaTrader, you've got a lot more people available to answer.
Also, it's free for users (not all platforms are). It's got reasonably good charting and technical abilities built in.
MT4 can automatically handle trades by monitoring the market second by second but since I am still not used it practically, can you please tell me whether you guys put instructions here? For example buy when the prices reach this or sell when the price is as such etc. ! or how it works? Is it possible to understand how it works before going live trade? I am currently practicing a demo offered by Oanda since I am a newbie and feel that I need time to start live trades.