I play tunes and sing songs at sessionas, so I think I am a shrewd idea why singers are not always mad keen on tune players. One of the reason I play tunes at sessions is,I admit, to practise them. This is not necessarily a good reason why I should, I know, but I do. there is therfore a motivation to jump in quick at the end of the previous person's contribution, and start a set of tunes. However, the urge to sing generally has a different motivation: an appropriate song floats into your head as appropriate to the mood of the evening. And of course, it is impossible to sing this song because some irritating bugger has just started some set of rigs or jeels the minute thhere was a moment's lull in proceedings. And by the ned of their set, either the moment for your song will have past, or some other irritating bugger with another set of tunes they want to practise will have started up. That's the way it goes. The best thing for a singer to do is to stand up, lurch sideways and fall onto the table, knocking over several drinks and emtying ashetrays on the floor. This causes the fiddle players to put thetor instruments away in a panic, or at the very least to clutch them protectively in their bosoms. this gives you a golden opportunity to start your song.