A profession is a vocation founded upon specialized high educational training (Wikipedia). For example, you can have a doctor union - it doesn't mean that every doctor is a member in it.
Part of this was also structural, if you think about it. the professionals were typically self-employed or partnerships. The professionals, in other words, were the bosses/upper management. The need for a union, somewhat redundant. Notice, that changes when the State becomes involved. Then you do see, say teachers unions. Hope this helps.
Historically, professions = Upper/Ruling Classes. Members of the ruling class don't (at least historically want/need) form unions precisely because they are/were the ruling class. [Edit: Professional Associations i believe were fairly common, as a vehicle to further the interests of a specific profession.]
Perhaps within the last 100 years, but not "historically" in a general or broad sense. The historical ruling class didn't have professions, they had power.
Up until 1812 or so, I would agree with you. But the landed classes were forced into the professional ranks throughout the 19th C. "To makes ends meet." The Corn laws, ca1830 & ff.
Edit: If I may elaborate on this.
Also, i did not mean the political sense of "ruling class". I meant, strictly speaking, their status as economic agents. If you are a partner in a partnership, you have legal control rights. Same as if you are a material shareholder in a stock-company. You are not an "at-arms-lenght-employee" in other-words. So, the idea that you would need a union for what were in essence "company directors" just does not make logical sense. Again, that changes when (whatever the expertise) thes folks are forced to work for the state; they are then stripped of their control rights and take on a position more akin to Labour, structurally.
I must agree that I specified too short a time period before which the "ruling" class simply ruled and weren't strongly connected to professions and investment activities.
