NETeller drawing

[NSchandler]

Basically it's because as you purchase more and more tickets, each ticket represents a smaller portion of the total number of tickets entered. Thus, its value is less than the previous ticket. Additionally, part of its value "cannibalizes" the value of the previous ticket(s).


Use small numbers to think of the intuition:

Suppose there are 3 tickets, not including your own.
If you purchase 1 ticket, this represents 1/4 of the total tickets available, so it's value is 1/4 of the total prize pool. The second ticket, however, represents only 1/5 of the total tickets outstanding. In addition, it decreased the value of your first ticket. A third ticket is only 1/6 of the total number of tickets outstanding...

Here are the odds of you winning with various numbers of tickets:
1 - 25%
2 - 40%
3 - 50%
4 - 57%

So the value of the first ticke is 25% of the prize, the value of the second is 15%, third is 10%, etc...

Anyway, this is the intuition at least.