My guess, it is because many SP do not understand that it is business and take it personal. For example, in general trade you can ask a person/company about specific job and the costs and can even ask for a discount or bargain over a price even when all the information about their company, services, and prices are given on their website. Rarely they will be offended and often will write a polite detailed response in hope to get your business. The same type of email in the same circumstances sent to an SP will, mots likely, lead to a rude response. IMHO, it is because many SPs do not separate business from personal life and take personal offence from business correspondence. I am not sure if it is because of self-selection of people into their line of business, inexperience (many SP are young), lack of training on interpersonal skills. Ia m sure SPs will say that it is because there are too many bad people contacting them, but, even it may be a reason, it is not an excuse for the rude behaviour of SP herself. But, of course, it is only if you want to consider it from a business point of view.