Buying a time share directly from the hotel or from the web?

I had just gone through the presentation at the Maui Westin Villas. The price tag was $40K+ for a 2 bedroom lockout every other year. I could not shell out that type of money but wanted to do more research afterwards. I came across websites that resells timeshares and the same thing was on sale for $17K (plus - the annual maintenance fee was much less via the web). Now, why would I or anyone for that matter purchase the timeshare via Westin directly??

I am just trying to make sense since I was sooo tempted to purchase via Westin.

Thank you to all who could shed some lights on my confusion.