Technically English (and I think all Germanic languages) doesn't have a future tense. The future is rendered as a mood in English, using a modal (mood auxiliary) verb, in the same class as (and mutually exclusive with) "can", "may", "must", "would", etc. The past and present tenses, on the other hand, are true tenses, and both in the indicative mood (no modal verb or the "do" dummy modal verb).
The logical basis for this distinction has to do with the concept of realis. Essentially that means what it looks like: realis moods have to do with 'real' things - things which are considered certain to have already happened; while irrealis moods are not certain for one reason or another. There's a general tendency in language to regard the future as inherantly uncertain, and thus place it in an irrealis mood.
Whether this is a peculiarity of Germanic languages or is universal among Indo-European languages is unclear. In Latin there is a future tense for the imperative mood (commands - an irealis mood) as well as indicative (events that are certain - a realis mood), but not for subjunctive or supine, two other irealis moods.
For trivia value: Caia does not have tense; aspect and mood are used to imply tense, and if tense must be made absolutely certain, it can be indicated with adverbs. It has three basic moods (more complex moods are specified with helper verbs or particles): indicative, potential, and hypothetical. As in English, the indicative is used for events considered certain, and is used primarily for past and present tense. Potential mood indicates that an event is possible, but not certain; it is used for the future, among other things (although the preferred method of referring to the future is to reduce it to a certain, indicative present expression such as "I intend to go" or "I want to go", which is more precise). The hypothetical refers to events that are known to be false (hence talking about a hypothetical, counter-factual "what if" situation).