It's all up to the marketing trend and business plan they have setup when they initially started their business, you will find many great shared hosting providers offering almost the cheapest hosting but charging way more than other for dedicated servers for instance, i guess simply dedicated servers is NOT their field !..
Also you may look into it this way, if you get a lot of happy shared hosting clients, eventually they will upgrade to a dedicated server with YOU ONLY since they already began to trust your service despite how costly your dedicated servers are compared to others, i believe there are other providers also out there who provide really quality services a bit costly than others but jsut worth it !..
also dont rush to any KNOWN hosting name and sign up for their services just for no reason, word of advise, been there, tried that with 1&1 Shared Hosting, they are not that good at all, as we faced multiple downtimes and weird server migrations which should not take place with a reputable provider !...