I can answer some of these questions; I used to work in a hair salon at their front desk and I had to learn about ALL the products. But I think the biggest problem is that people just don't know HOW to use a shampoo bar. Maybe a video tutorial/introduction to just how shampoo bars work would help take away some of the intimidation.
1) Course, thick, long hair takes a lot of effort to wash because there is just so much of it and you have to get the shampoo everywhere without missing any space. I liquid shampoo SEEMS easier because it's already easy to spread.
2) I've heard that complaint about regular soap bars, so it's really just about educating them about proper storage of bar soaps to begin with.
3) Coloured hair can be tricky; most commercial shampoos, specially current salon shampoos, are being formulated to protect colour in hair. It's more about something being less stripping as something to protect the hair colour. Previous shampoos of yesteryear contained ingredients that were very stripping to the hair. The way permanent colour works, is that a base (ammonia/bleach) penetrates through the hair strand and "removes" the natural hair colour, and deposits the new colour in it's place. Because hair isn't alive, it won't repair itself, unlike skin. Once that damage is done, it won't be undone. And once there is damage, it's easier for the damage to get worse. Like if you get tear in your sweater, if you leave it alone, it will be okay; if you pull at the loose strand, it will get worse and unravel. That's why if you have split ends, you need to have them cut off or they will split even more up the hair shaft; like a run in a stocking. So, because the ammonia has already created "holes" in the hair, those "holes" can be where the colour is stripped away with harsher shampoos. Again, educating people around ingredients could help that, but you can't force people to learn if they don't want to.
4) Similar to #3, it's only recently that shampoos are using ingredients that are less aggressive and agitating. If they were more knowledgeable in ingredients, it might help. But sometimes if you have allergies, you stick with what you know doesn't create a reaction; just to be safe rather than being sorry.
5) Grey hair is a different hair texture to natural hair. It is often courser and dryer. People with grey hair often need high hydration shampoos.
6) That's just being entitled. *EDIT* I like
@Ford 's idea!
7) This is a culmination of much of the answers above. Salon shampoos are a higher concentration than drug store shampoos. To pull arbitrary numbers out of the air purely as an analogy; you could think of it as the salon product having 40% water, where the drug store product could be 90% water. (Again, those specific numbers are arbitrary). You will need less of the expensive stuff and it would last a lot longer. Also, many people find they can go longer between washes when they use the higher quality stuff, extending the life of the product even more. I got a lot of free [very, VERY expensive] shampoo that I'm still using today, five years after I left. And I can easily go another five, if not more. One 250ml bottle lasts like 2 years.
8) I mean, everyone has different financial situations. I'd probably say the same thing if someone tried to sell me a Luis Vuitton bag! But we can't satisfy everyone; these just might not be the people you get to please this time, and that's okay!
9) It might depend on living situations. For example, residence/dorm life, you share the bathing facilities and you have to bring your stuff every time you use it, and you have to take it with you. Or, they may not have the storage space. Maybe a soap dish would be the answer?
I hope I was somewhat helpful in giving one perspective. Again, I think it really just comes down to people's general lack of knowledge regarding the subject. I mean, there are people all over the internet that don't think bar soaps are hygienic! I'm not sure how active you are in using social media with your soaps, but if I were you, I would try and spread knowledgeable information so consumers can feel impowered to make an INFORMED conclusion, instead of a subjective one.