The free tools for PIC or AVR are not that simple to use, as compared to MCS51 tools.

Take for example, you have a HEX file, and want to flash into CPU.
For that, you should have a thorough understanding of all the fuse bits even before you test it out on your hardware...this is not the case with MCS51.
Added to this is the classic inverted fuse bits in AVR, which stands for 1=>fused, 0=>not fused.

Because, of these fuse bits, I was away from PIC and AVR for 6 months. Within the time taken for studing them, I could complete 2 products using MCS51. When I reached a dead end with MCS51, I studied PIC, and to some extent AVR.

Plus, you have to get familiar with a whole new architecture, the way it works,....quite different from what most engineers over here already know. They are very comfortable with 8085, MCS51. These are covered in their study course.

Plus, help is easily available from seniors,etc., especially from an excellent forum as 8052.com for support.