I flew as part of a group of 8 once MAN-IST on TK. Apart from us, there were 3 other pax.
I always used that as the argument for why private carriers were more efficient - but to their credit, TK have now added BHX-IST, and are one of the world's fastest growing carriers (I'll ignore the stupid football player ads though).
Winair puddlejumpers are regular single passenger taxis, but only 19 seats to fill on a good day anyway! Always amused how busy SXM to SAB gets on Wednesdays because everyone goes over to renew their car tax there for a fraction of the cost of what they pay on SXM! I guess in a way, that's a reverse PSO!