This is going to get complicated, but bear with me.
Let's start by looking at the two roles that the Speeder Bikes are likely to play in an Imperial Operation. From the movies we know they are used for:
Scouting/Patrol When scouting, it's important to be able to blanket transmissions. You don't want the people you are poking at being able to report back if they spot you before you can eliminate them.
Hit and Run Attacks Due to their speed and built in firepower, it's natural to assume the speeder bikes would also be used in hit-and-run operations. Again, you want to suppress comm transmissions so that reinforcements don't arrive.
In the one battle we see them in, they are fighting very angry teddy bears, so we don't have a real perspective on their use in battle because the obviously technologically inferior bears weren't using comlinks to communicate. (It's much more difficult to jam a converted-animal-horn. I won't cover that here.)
So let's talk about modern jamming technology. Electronic interface can come from just about any source. Your microwave, your mobile phone, your electric oven. Even a Fish Tank can interfere with wireless signal operations (looking at you, Admiral Ackbar). You can demonstrate some of these effects in your own home with an AM Radio. This involves walking around your house playing with the tuner on an AM radio by hand. Keep this in mind, it will be important later.
The point here is that jamming ALL signals is vastly easier then jamming a specific signal (frequency) - but even jamming a specific signal can cause 'bleed over' into nearby frequencies if the transmission is too powerful.
For an example of this in the Legends universe, Han Solo once installed a jammer so powerful that it jammed his own systems and his ship was only saved because it was SO powerful, it burned itself out.
But let's look back at our first discussion about how speeder bikes are used. You're traveling at blistering speeds on a device that is apparently both fragile and prone-to-go-out-of-control when damaged in a combat environment while shooting and being shot at. Do you have time to pull out an AM Radio, identify the source of the transmission, and the frequency, and then adjust your dial to jam it specifically?
Electronic Warfare is something that the US Navy engaged in regularly during the Vietnam war, which led to the development of the EA-6B Prowler, a dedicated electronic warfare plane. It's role was to target specific electronic systems and 'blind' them while attack aircraft approached.
Speeder Bikes have a crew of one and travel at blistering speeds. Prowler's have a crew of four and travel only at subsonic speed (not implying that the Speeder Bike is supersonic, just pointing it out for comparison).
TLDR: It seems much simpler (and cheaper) to give Imperial Scouts a one-switch-Jam-everything (Including their own comlinks) system then to equip four of them with a 50 million credit fighter that can do the same job.