Maybe it's not just explosives but going through permits and paperwork and such. I imagine there are also other costs like insurance, because you have to be covered if something goes wrong, and if you're blowing stuff up with dynamite, the premiums are probably high. There could be fees to the city for traffic closures. Also, knocking it down in one go leaves a big mess. There is also the expertise: you can't just stick dynamite wherever you like and detonate, or the thing will go sideways into another building. Charges are placed onto specific structural supports, and denotated in a proper sequence.
> you need to spend a fortune for the explosives and the license to use them, as well as demolition experts and all sorts of insurances
Depending on the personal injuries claims that courts hand out, this could be risky in some countries.
If it takes the guy just a month to get the job done, it should be a competitive method here in Sweden too. I'd love to se a more detailed analysis of the costs involved in both methods.