All of these things are done to change the incentives about something, you can't expect them to be consistent without reference to those goals (and even then...)
"In a tax system with progressive marginal rates on annual income, treating income resulting from action over multiple years as earned in the year realized results in a artificial increase in the tax burden on those with that kind of income pattern. So, there's a sense in which treating capital gains earned over multiple years differently than capital gains earned over a single year or less (the latter taxed as general income), given the progressive nature of the tax system."