From what I have read on the topic of the G spot, I think the problem is that the glands vary in size and position and are sometimes close to the top of the vagina and sometimes far away. If close then it is easy to stimulate it and so cause an ejaculate. If far away, it is harder to stiimulate - imagine wrapping your clitoris or penis in layers of bubblewrap before trying to bring yourself off. Its much harder to achieve an orgasm this way. Some women may have only one layer of bubblewrap between the vagina and the glands, others may have many more.

This means that, while most women do have these glands, not every woman has them in an 'accessible' location for intercourse. So, it is hard to test the existence of the G spot because there is not a consistent response from all women. The only way to prove that this gland is the g spot and responsible for female ejaculate is to perform some form of surgery and manipulate the gland directly and note the effect and I am not sure there are many women who would volunteer for that procedure

Clitoral and vaginal orgasm are linked to the same organ. The clitoris is a large area of erectile tissue that surrounds the vagina. The sensation you get when the vagina is engorged and a penis (or hand or tongue or whatever) is inserted is stimulation of this erectile tissue. What we call 'the clitoris' is actually a small protrusion of that tissue poking through the muscle layer. Around the vagina it is buried in more, less sensitive tissue but here it is more exposed. Therefore, stimulation of the clitoris is more acute and intense.