Why do you have a bed if not for going to sleep in it? Does it mean a tradesman can pop in there for a nap, or lay down if they feel a bit fragile?
Why do you have a garden if not for people to use it? Does it mean any random can come and suntan or let their kids play in it? (see another thread...)
They're for the private use of the householder and anybody they've chosen to invite into their home.
Somebody coming to service the burglar alarm most probably doesn't need to stay overnight, so they won't need the use of a bed, but they might need a toilet at any time: sleeping times are normally planned in advance, but this luxury can't be guaranteed for most of us when it comes to needing to use the toilet.
I agree with PP that many people look down on tradesmen, and it's a horrible attitude. Thread after thread on here, people complain about tradesmen parking their vans in the street outside their homes, but suddenly those same people have no problem at all about the plumber parking that same van outside their home when they need his services. Tradesmen are humans too, and they need drinks and toilet facilities like the rest of us.
Maybe the government should bring in new legislation stipulating that, when a tradesperson is invited to your home to do work for you, it is incumbent on you to provide adequate toilet facilities for them and inform them on arrival of the arrangements. Most of us would just say "no problem - of course he's welcome to use the loo" but those who object to this can, if they prefer, arrange and pay for a portaloo to be installed outside their house, just in case it's needed, and then to be taken away afterwards.
I'll bet that would suddenly make people decide that letting somebody nip to use their toilet for standard toilet-based duties is actually not a problem after all. I'm only half-joking, really - most other professions have basic workplace rights guaranteed in law, so unless we train robots to completely replace all workmen, why should they be discriminated against? It's a good thing that most tradespeople tend to have a practical turn-up-and-get-on-with-it attitude rather than spending ages fretting over such unimportant fripperies.