This answer comes down primarily to "What about..."
This is the biggest one
Why is your Decker not in the field? The ability to hack the stuff in the run location requires that he get in close physical proximity to it. That's how the SR5 Matrix works. The whole "I'm a Decker who sits and home and does all my work remotely" doesn't fly in SR5, because of the Noise mechanics. The further you are from something and the more stuff is in between you and the thing you're trying to hack--the bigger penalties you take to trying to hack it. Any site worth their salt knows this and would set up countermeasures (like walls, Em-blocking paint, landscaping, a Faraday Cage, or just by putting important things away from the exterior of the building) that prevent someone from hacking into their stuff from outside the building.
In short...in SR5, a Decker can do some work remote--such as setting up fake IDs or getting blueprints and so on...but they can't mess with the cameras, control locks, disable security systems, shut the alarm off, break into a computer for a datasteal, or anything else like it without being with the team breaking into the building.
And that's not to mention that some security systems, data repos, etc. are offline and thus cannot be accessed without a direct physical connection to that thing.
And no, 'routing' through a friend's commlink doesn't work, because you get all that Noise trying to connect to them, too.
Does your Decker not realize how useful they are in dealing with other sorts of obstacles?
- A goon with a giant Smartgun is a lot less scary if his Smartgun gets bricked.
- A Decker who takes over the Cameras or security sensors can provide live-intel to the party
- If the alarm goes off, the ability to fake where the alarm says intruders are can buy you time, or fake a false-alarm message
- Drones are much less scary when the Decker keeps subverting or Bricking them
- Whoops, did that massive cybered up troll forget to turn the wireless off on his Cybereyes? Guess he only gets to see what the Decker wants him to see.
Probably the most common job in the SR world is the datasteal...get in, get your Decker close to a secured data repository, then let them hack into it and steal it. Because of the Noise issues mentioned above, the Decker must by with the team because otherwise he would be operating at something like a -200 dice pool.
Deckers, by necessity, have high Logic. This also makes them well-suited to be good at any of the Mechanic skills, as well as Medicine and Demolitions. Any of those skills can be useful on the actual run...especially if no one on the team has those skills.
The ability to cleanly sabotage a piece of tech requires that you be able to understand that tech and know how it works...Smashy the Street Samurai can break the thing, but sabotage that makes it look like it failed on its own requires skill in working on the thing you're trying to sabotage.
This doesn't seem like a DM-style issue to me. If I had to guess, you're ignoring the Noise rules, and that's what is causing this issue...if the Decker doesn't have to go with the team to do their job, then of course they are going to do it all remotely then sit safely at home. That's kind of the whole point of the Noise rules--force the Decker to actually go on the run with the rest of the team