Asking from a US perspective. It seems like every blue-collar profession has a union: plumbers, roofers, boilermakers (?!), etc. Why didn't white collar professions develop unions?
There are some exceptions (teachers, Hollywood writers, etc) but the majority of labor unions seem to be blue-collar.
I'm not sure if there is a historical reason, but I can explain the business ones.
The strength of a union comes from it's collective bargaining power. A single blue collar worker quitting isn't much of a threat, all of those workers quitting is a serious threat to business. By threatening collective action, the union can bargain for higher wages and benefits from their employer than they would otherwise be able to get.
There isn't that much fundamental difference between two blue collar workers. Sure one may be better than the other, but the differences would be small compared to two white collar workers. White collar workers draw bargaining power from their own individual value. They each have a set of skills unique to them, and are valuable on an individual basis. An employer may not care about a single plumber quitting, but they would care about their talented accountant quitting.