The use of stranded cable is listed in the power requirements doc. Power is being run across multiple pairs to help distribute the load. If a pair get broken, this then leads to the remaining pairs to take up the slack.
Using stranded cable makes the cable more flexible thus less prone to breaks as the cable gets bent, flexes...etc... and helps with distribution of the load. While no one on this board can force or make anyone use one cable type over the other, it has been stated in the power requirements doc to use stranded. If anyone decides to use solid core, then that is your choice but if you start to have issues, don't say that you were not warned.
Bill