I also think that it takes a different personality to work outcalls, than it does to work incalls. Girls that are not as extroverted may not feel comfortable working outcalls due to the fact that you generally have to take charge in those scenarios. Incall girls can still be introverted and remain within their comfort zone at the incall - they would be in charge of everything that happens thus, feeling safer. The vibe of an outcall is totally different than an incall IMO. Incalls can also provide a little more anonymity than outcalls so for girls that feel that their discretion is of utmost importance, they may choose to work an incall instead of out.
It irks me a bit to hear that incalls would be considered assembly line whereas outcalls would not. Outcall girls can work the same volume as incall girls. The premise of an 'assembly line' should only be used when referring to mechanical service, incall or out.
![Wink ;) ;)](data:image/gif;base64,R0lGODlhAQABAIAAAAAAAP///yH5BAEAAAAALAAAAAABAAEAAAIBRAA7)
There are plenty of lovely incall providers who (whether they are agency girls or independents) manage to provide unique experiences while SPing. ^_^
Outcalls are generally preferred due to them being legal vs. Incalls not. There is a lot of tip toeing the fine line of legalities - and many would prefer not to play with fire.