What is the point of this add-on in this tourney?

[growlers]

Sorry if this is low content, but I was just reading the "strip poker" section on card player and this is a quote:

"Every Monday, Wednesday, and Friday at 6:30 p.m., Mizrachi is available in the Planet Hollywood poker room for a question-and-answer session. The tournament begins immediately afterwards at 7 p.m. It is a $50 buy-in that gets players $1,500 in chips, but players receive an additional $2,500 chips for an extra $10 add-on"

So it is clearly silly to offer 2500 chips for only 20% of what the buy-in is for 1500 chips - no one would be stupid enough not to take it. Why not just make it $60 for 4000 chips?
What do they structure it this way? Is there some silly obvious thing I am missing?
I understand when tourney's like Binion's is say $90 with a $60 rebuy, so people will think it is a "cheaper" $90 tourney, but I've never understod this add-on stuff.