Welcome. I fully understand the feeling, it took me awhile to wrap my head around the sheer amount of money spent at these things.
Name recognition and expertise are the main factors IMO. From what I've seen organizers genuinely want their folks to attend, whether it is because they want their money, to provide training, or both.
You can find upfront conference prices starting at over $1K per person with yet more money spent by companies wanting to promote their own products at the event.
Met Laura Bush(briefly always briefly) while working security for an HR show(SHRM).
https://annual.shrm.org/sites/default/files/SHRM17_Reg.pdf
https://en.wikipedia.org/wiki/Society_for_Human_Resource_Management
~15,000 attendees * ~$1,500 = ~$2,250,000
I don't know what Mrs. Bush asked for, if anything, but $200,000 would have been easily affordable.