I think my motivation has changed over the years. Strangely enough for many years I was severely embarrassed at having to speak in public. By chance I was on a course (in-service) and had to give a brief session to the rest of the class. I sweated over it but it went okay and the instructor suggested I should look at education and training. So it was initially a challenge for me. Now though I agree with Jac, it’s the immense satisfaction I get when even one of the learners “gets it” and you can see it on their face right there in the classroom.
That old curmudgeon GB Shaw, yes him of the “those who can..” calumny, obviously never experienced it!