It isn't just some hobbyist doing this - drones are programmed to prevent them flying with 1km of an aerodrome. This would have had to be disabled to get so close to Gatwick. They can't be shot down as they are tiny and moving about all the time, as well as being a few hundred feet in the air, pretty tricky. There is a reason there is a big penalty for people who do this. Stray aircraft wander into major airports airspace, they can't be shot down either, and aircraft would again hold, divert or be grounded.
The problem as always is that "the public" feel it is their right to fly drones if they want to. Many aircraft have had drones flying much too close to them, usually the drones aren't traced. There will be a major drone-aircraft collision at some point.
I suspect that as this is 2 drones, and they've been going for more than 12 hours, they must be professional ones, and they must be returning somewhere to be recharged, perhaps there are quite a few of them working in relay.
Safest option is always to close the runway; yes it causes a huge amount of disruption, which usually the airlines have to swallow. But no-one wants to be the first to have a drone fly through their engine, or break their windscreen/ flight controls/ hydraulics.