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It is all a matter of cost. Consumers shop for price and not performance. There is an old saying that, "Hay is cheaper after passing through the horse."
The MOS transistors are scalable (you can play with its dimensions, for BJT the dimensions are usually fixed) and smaller. In addition, logic gates with MOS are simpler (and smaller…. again). Finally a MOS process is cheaper than a bipolar one.
1. From ground to supply swing in output (fom rail-to-rail)
2. High noise immunity
3. Low power consumption
4. More concise chip area due to lower power dissipation
Well, one should be careful in stating that circuits using MOS transistor will have lower power consumption. While this can be true for digital circuits (in CMOS gates there is no static power consumption), it may not be true in analog circuits, where the larger gm can be achieved by BJTs, for the same current. Moreover faster analog circuits use (almost) always BJTs.
when u use CMOS you can work on very small area, the size of transistors can be personalized to your application, high input impedance, the posibility to implement them as conmuted capacitances in to replace resistances, lately they can work on sub-theshold to minimize power consumtion increase noise rejection, etc...
this family has no critical voltage limit. (3-18Vtyp)
and low power consumption.
i made a circuit using about 35 CMOS ICs.
it took only 1 mA.for all ICs
there are a lot of good reasons: it has a simple fabrication, high speed, low static power consumption, a higher integration is posible (there arenot resistive elements -resistive elements require large chip areas in BJT-).
Well if you look at it purely from a performance standpoint, ie., spped, BJTs win hands down. Their fT is much higher than CMOS. However a majority of todays chips are digital with ~ 20% analog. For use as a switch the MOS transistor works the best. It has zero DC consumption, much smaller and since the late 80's is easier to fabricate.
If it was left to analog design engineers, they woul always go for a Bipolar or atleast a BiCMOS process, because it gives you more options
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