I think the word "lack" is arguable!
IMHO, a lot of adjustability = flexibility => user friendly.
It is a matter of how to design an intuitive interface which naturally lead user to find where he/she can adjust a feature. i.e. It is "easy to adjust the program" which matters, and easy to adjust is very different from only a few things can be adjusted. Keeping adjustability low is quite a negative way of doing.
I have played around for quite some time, evaluating Total Commander, D.Opus, XYPlorer and xPlorer². I was hesitating to choose xPlorer² because of not enough "adjustment" user can opt to, especially for its toolbar.
Among all D.Opus offers MAX level of adjustment... but IMHO, it fails to offer a simple way to let user find out where and how to achieve something.
Among all, Total Commander offers the most intuitive interface. However, I did not choose it because it is not unicode aware and it does not support ADS.
xPlorer² sits between the two. I just bought my xPlorer² license today

But in term of adjustability, I think it is at the min edge... in my opinion, it has the fewest adjustability to offer... and I don't think this is a good thing.
TC impress me by its powerful toolbar which is user definable (including button icon and icon size) and its super intuitive mass rename interface.
XYPlorer impress me by its right-click options for different column header. (e.g. right-click "size" column, you can choose different way to display file size)
All these are good features which I hope xPlorer² will one day incorporates and further improve them.