It is not that they are "less picky" ... it is that in Compulsory routines, perfection has been established. The judges know where every kick, hand movement, specific pose, skill, etc is supposed to occur in the routine. If you change the order, or have your hands facing down when they should face up, do the "wrong" type of turn (it should have been a pivot turn and the gymnast did a heel-snap turn, for example), then they deduct.
In Optionals, the judges are looking for form on the things the gymnast performs... and does it flow... and artistry... and did they meet all of the requirements for their level.
Lets say that someone did all of the skills and poses in a L4 floor routine PERFECTLY, but did them out of order... and a L7 gymnast did all of the skills and poses in their routine PERFECTLY, but did them "out of order" ... the L4 would incur deductions. The L7 (as long as the new order worked with the music) would not incur any deductions.
So, for those who are not technically perfect, often times, they are better Optional gymnasts than Compulsory gymnasts.