Thanks for your responses, but I still have no clear idea of why this is so difficult for me. I've replaced a lot of the fuel line in the boat over time and have the same problem with almost every connection.
1) the hose and fittings ARE all 1/4".
2) there is no issue with pressure in the line (many of the lines aren't even connected on the other end.
3) I've thought about changing to a larger size fuel line, but its too late for that now. I have too much new 1/4"line installed.
4) Coating the ends with diesel or oil does help, it changes the problem from impossible to aggravatingly difficult.
5) Getting them off requires a knife, even some that have gone on halfway and refused to go farther.
6) a little heat helps, a lot helps a lot. Maybe I should move to the tropics.

So I think Todd hit on it with his comment about the newer A-1 lines being stiffer, particularly in the small sizes. So I will continue to dread any project that requires changing a fuel line.