This is happening because there is unspent money in your league. During the free agency period, the game adjusts players' demands to try to eat up the available money. Whether it SHOULD do that (no) is a matter of debate, but nevertheless...
Personally, I would prefer that the game just let the owners pocket the extra profit and keep player salaries roughly in line with the user's chosen settings, but such is not the case. Some small deviation and gradual inflation would be tolerable, but I've got guys asking for 40 mil a year and it's only the third year of my league.
