This isn't just a president. If, for example, this was used by the president and their protection detail to coordinate routes, that might work. However, the stated purpose was to be used by campaign officials so that things like the Iranian attack on them don't happen again. Campaigns are made up of lots of people who are not trained in security or anything else, working in all sorts of places doing unplanned things. It is more difficult for them to adapt to restricted methods and they're the kind of people who aren't eager to adopt that in the first place.
A campaign is a lot like a company. Consider what would happen if you had to convert an employer to a restricted communication system for all internal messages. If it was a small company where everyone was knowledgeable about security risks, you could probably do it. I think you can imagine how hard it would be and how many people would ignore you if you tried the same with managers who don't want anything that will slow down their messages, technophobes who have become comfortable with something and resist any change, and processes that are considered critical and indispensable which don't yet work through the system you're trying to switch to. I've had to do it before and, even more frequently, I've had to watch the IT people try it and struggling to implement something against organizational inertia, then catch all the people who deliberately bypassed their policies.