People these days tend to favour a certain brand, and those who like Sebos know that although they are old fashioned, they are very good and reliable vacs, and so are prepared to pay a bit more for them.
Those who love Dysons, of course they would look at a Sebo and sneer at it thinking it was a relic from the 80's - but Sebo still has a lot of devout fans.
Look at how old fashioned Kirbys are - but there are still a lot of people out there who would never own anything else but a Kirby, and still seem prepared to pay a fortune for them - although more people now would only be able to afford a second hand one.