So, Snapchat has had these for a while, why buy the patent now? Word on the street is that Facebook "100% wanted [the patent]" and was in talks with the patent holder over obtaining it. We assume that, thus far, Snapchat was paying royalties to Mobli for using the technology. We will also go ahead and assume that Snap is a bit annoyed at the fact that Facebook previously went ahead and... eh... "borrowed" the Stories concept and proceeded to implement it across its most prominent apps — Instagram, Messenger, and the main Facebook app. So, as soon as Facebook appeared to be interested in a patent, which Snap is currently using, we can see how the latter would go "No, no, Fox stew is not for you!".
It seems the yellow ghost company really wanted to buy it, too, since it set a new record for the highest amount of money spent on a single patent in Israel (Mobli's home country). Previously, that amount was $2.7 million — a full $5 million less than what Snap paid.
Reportedly, Snap wanted the patent in order to have something to defend itself with in possible future lawsuits. It probably doesn't want its geofilters to get snatched away the same way stories did.