This particular aspect of microeconomic theory is known as
price discrimination. If I am a business I want to charge people according to their willingness to pay, as long as I can do so profitably. If Bill Gates walks into my shop with a headache, it probably makes little difference to him whether he pays €1,000 or €1 for aspirin. However, it might make a big difference to my business.
One means of discoverying what a customer is willing to pay (and some economists do not regard this as "true" price discrimination) is to offer some small additional frippery to your core product at an inflated cost over and above the worth of said frippery. Stewardesses that smile, a few inches of extra legroom and free drinks are not worth an extra €4,000 to most people - but "most people" are not the target market segment to which business class seats are sold.
One reason perhaps that Ryanair do not engage in such price discrimination (although they engage in plenty of other forms of it - see what it costs to buy a Ryanair ticket at the last minute) is that the people who fly BA 1st class would probably never be caught dead flying Ryanair anyway.