Actually, it's a whole lot easier to build a reliable receiver for one-way communication like TMCC, evidenced by the far fewer issues getting signals distributed in a vast percentage of train layouts. DCS, OTOH, with the bi-directional communication has some pretty tricky communication issues at times.
The other bonus is the TMCC signal lends itself to a fairly simple booster to aid signal strength, DCS would be very difficult to boost it's signal as you'd have to deal with each locomotive with the return signal. Also, the two-way nature of it requires a far more complicated booster, and you really need to be able to tap into the TIU logic to know when to boost in what direction.
Both systems have their advocates, and each one has advantages and disadvantages.
If I'm called on to just show up at a layout and add command capability, I'd pick TMCC/Legacy, it's easier to get running regardless of the wiring on the layout.
In order to get DCS running on layouts, especially larger layouts, you have to drive sections from unique TIU channels that are isolated from other sections. You also have to adhere to wiring practices to avoid signal reflections that scramble the track signal. Obviously it's possible to do DCS on a large layout with good reliability, but it does take more care in the power wiring and power district planning.
