All but Marco Rubio have wildcard certificates without an apparent use for them. It looks like whoever built their websites was keen on using all the budget they were alloted.
Who cares, their budget is in the millions. Better to spend the extra couple hundred bucks, and have it. They will most certainly need it (ex. donate.hillaryclinton.com, debates.hillaryclinton.com, vote.hillaryclinton.com).
The pervasive mindset is that mailings, tv/radio ad spots, and other traditional media platforms have a known and predictable return on investment. Using the web for organizing and fundraising is the new kid on the block. Despite the impressive showing in 2008 and 2012 on the Obama campaign its not a known/repeatable representative showing.
Every dollar spent on your web presence needs to return 5$ or more to funnel into these more stable predictable forms of outreach. Its not enough to be self sustaining or slightly profitable.