Sellers can split their tickets in different combinations. Often, they don't want be left with a single ticket. This means you may not see the option to buy 3 tickets if there's 4 in a listing.

Looking for a specific number of tickets? Use the filters to find listings with the number of tickets you want.
 
Desktop: Choose how many tickets you want under Number of tickets
StubHub app: Tap Filter and then the number you want