Why is that? Getting the CMS out of their way is one of the primary reasons they outsourced development (or implementation, or whatever) to someone else (agency, freelancer, whoever).

If what they're using day-in and day-out is in their way or not "simple to use", its hindering (to various degrees) their progress in doing what they want to do.

If I make a website for a musician, they want to probably publish musician / band related stuff and go on making music; if they're having to figure things out or call me every time they log in... I've done a very, very bad job at giving them what they need.

I can't say I've ever had a client comment to me that the system was difficult / non-obvious, especially when using WP (even the first few I pushed that used almost vanilla WP admin).