WDM vs fiber

If I understand it correctly, WDM (CWDM/DWDM) can split your optical signal into different wavelength, which in turn increases the available bandwidth in a fiber cable. I know there are different types, which can utilize more wavelengths and so, but the idea I guess is the same. This obviously requires some type of equipment (e.g. multiplexers). If I understand it correctly, WDM is mostly used for companies, and not end-consumers like you and I. Why is that ? If I'm not mistaken, WDM assures the bandwidth you are paying for, i.e. you don't have to share with others, since the bandwidth is allocated to you.

And since this is the case (at least I think it is), does that usually means that you have some larger centrals, connected to the WDM transport network, which are then connected with regular non-WDM fibers from smaller centrals/end-customers, which are then multiplexed into several wavelengths when entering the WDM network ?

I'm just trying to grasp the general idea behind WDM. It sounds awesome, so that's why I'm wondering why it isn't everywhere, and not just in the transport network. Is it cost ?