Why are they useless? Could they not carry a payload, and swarm their way past defenses that aren't equipped for "volume"?
Urban radio environments are crowded, not actively hostile.
The issue with high energy jamming (broad frequency band denial) is it makes your jammer a super tempting (and easy) target for a HARM or equivalent, and consumes quite a bit of power. If someone is actively denying such a wide frequency band, any high school level electronics student can design a pretty effective seeker.
And the whole 'radio power drops off as a cube of the distance' thing means the equipment needs to be pretty close to operations, so it's going to get attacked pretty often.
The noise level in a typical urban environment from wifi is already pretty terrible, 'hostile' or not. Way more terrible than a typical remote environment, which is where these drones are being used, unless there are active countermeasures pretty close.
Counter measures, counter-counter measures, etc. But I'm not seeing much mention of effective jamming happening in-theatre right now.