Simply announcing a presidential candidacy, or even appearing in primetime presidential debates, offers no assurance that your name will appear on ballots come election day. All 50 states have their own ballot access laws, many of which are onerous even for major party candidates.
For the 2016 elections, presidential campaigns will spend $1 to $2 million each to get on the ballot nationwide. Then there's the man-hours required: While some states — like South Carolina, with its $40,000 fee — want money for ballot access, others — like Virginia, which necessitates 10,000 petition signatures allotted across congressional districts — require significant time investment from campaign staff and volunteers. (Virginia's rules kept all Republicans but Mitt Romney and Ron Paul off the ballot in 2012.)
Because of the monumental effort required, some major party candidates will not be on the ballot in all 50 states come primary season. Republicans Jim Gilmore and George Pataki already missed the filing deadline for Alabama, and all but the richest campaigns are unlikely to meet the requirements for every caucus and primary election.