How come publicly available standards have been tied to patented techniques? Doesn't this give the patent holders a monopoly position?

Most standards bodies have rules about patented techniques, and other so called intellectual property, required for the implementation of their standards. Some require that none of the people developing the standard know of any patents which may be needed. Some may require any patents held by members be licenced freely to anyone. More commonly, standards setting bodies require their member organisations to offer any related patents under reasonable and non-discriminatory (RAND) terms, to anyone who wants to implement the standards. Of course, the people setting the standards control the patents, so they pay nothing themselves. Also, free software generally cannot bear any patent licence fees. What is reasonable for one group may be quite unreasonable for another. In all cases, there is the possibility that a third party will show up claiming patent control over things in a standard. This is how things currently work. Live with it.