Maybe they choose long domain names because every other shorter option is already taken? While I understand the preference for short domain names, long ones can be fine if they are memorable. Most people will either find the website by a search engine, click on a link somewhere, or access it through their own bookmark. So they won't be typing the full domain name anyway, so long names are not so much of a detriment.
Brand preferences - sometimes a company wants to be tied with a brand and there isn't a suitable domain that is shorter. Another example I see trending is from people mislead to believe that a good domain should be keyworded at all costs. There are a lot of people providing inaccurate information and subsequently a lot of people taking this information as a sure fact.
A lot of spammers and other unsavory sorts will use longer names since they don't have to be memorable (though I'm not trying to imply that all long domain names are malicious), especially if they're using a domain generation algorithm. But regardless of that, with new generic Top Level Domains (gTLDs), you can get that shorter domain name you wanted at many more TLDs, now (e.g., .bargains).
More than likely it's to develop an EMD (exact match domain).. For example, if the term "low cost internet web hosting" were getting 5000 searches per month.. It's not much, but might be one someone could rank for a little easier with "lowcostinternetwebhosting.com"..They would register and develop it in hopes of accomplishing that. At one time, Google would give more authority to EMD's.. However, that isn't really the case anymore.