The Special Forces are an expensive force to run. Higher pay, training, equipment and travel costs make it some five times as expensive, man for man, to run a Special Forces unit versus a regular infantry outfit. For example, an A Team has one officer (a captain), one warrant officer, and ten sergeants. The army has nine enlisted pay grades (E-1 to E-9). The ten enlisted men in an A Team include one E-8, five E-7s and four E-6s. Your typical infantry squad was led by an E-6, with the help of two E-5s. Everyone else is E-4 or E-3. The Special Forces troops have also been in the military longer than your average infantryman, and in the army, pay goes up the longer you are in uniform. 

The higher ranks in Special Forces units unavoidable. The men who make it through all the Special Forces training are highly promotable no matter what unit they are in and it's understandable that the army simply organized the A Teams with positions reflecting the rank that these men would soon reach. Moreover, the A Teams were also designed as training units, so you can think of each of the members as experienced instructors (which is what they are) who would normally be of higher rank. The Special Forces situation is not unique, all elite commando organizations have the same problem, and generally apply the same solution. Indeed, some countries have more officer positions for their commando units. 

The Special Forces may add more officers to A Teams, although using Warrant officer ranks rather than commissioned ones (the people we normally think of as officers). Warrant officers are an ancient practice that has exceptional NCOs promoted to "Warrant Officer" rank. These positions ("Warrant Officer 1, Warrant Officer 2, Etc.) parallel the pay of commissioned officers (Warrant Officer 1 gets paid about what a 2nd Lieutenant does, and so on), but the Warrants are technically outranked by all commissioned officers. When a sergeant first class (E-7) with ten years service gets promoted to Warrant Officer 1, his base pay goes from $2,250.10 a month to $2,423.10. Not much of a raise, but officers and enlisted men now call him "Mister Jones" (instead of "Warrant Officer Jones") and troops have to salute him. The Warrants can also go to the officers club, although many prefer to continue hanging out at the NCO club. When the A Teams were first organized, there were two commissioned officers. But it was soon realized that a senior man was needed to be the executive officer of the team. The team leader was, at most, a captain, and often just a lieutenant. The executive officer was always a lieutenant and most of the enlisted members of the team usually had more experience and leadership ability than the officers. So the executive position was changed to a Warrant Officer slot and the most experienced Special Forces NCOs were promoted to fill these jobs. The Warrant Officer on the A Teams provide adult supervision, as all NCOs do. Even A Teams sometimes need an old hand to keep things on an even keel.