Economists are constantly looking for better ways to model the behavior of economies, but some are still hesitant to give up macroeconomic theories. This is partly because they don't want to lose sight of macroeconomic theory's emphasis on markets as the main source of economic activity. It might also be because the more complex models require more assumptions, which are inherently more difficult to come by in a dynamic model.
Some micro-economic theories, such as the theory of optimal currency exchange rates and endogenous money demand, require that the market price of a commodity is constant in time, and therefore that it can be used as a gauge for calculating expected prices in the future. This is an assumption that can be difficult to come by in a static model, because the changes in supply and demand of a commodity do not occur at the same rate over time.
Dynamic macroeconomic theories, on the other hand, rely on information that can be obtained from historical data. These models take data like market data, economic growth rates, and fluctuations in inflation into account, and use it to make predictions about what the economy might do next. Dynamic models often have a large degree of complexity, so there are many assumptions that need to be made.
Macroeconomic theories usually involve assumptions that are not made in micro-economic theories. One of the most important is the assumption that money is always in use and that there are no changes in monetary policy in a market economy. However, with micro-economic theories, changes in the amount of money in circulation or in the level of interest rates would not affect the economic data, unless they were very large and lasted a long period of time.
Micro economic theories rely on the assumption that the supply of money equals the demand for it, and so they have nothing to do with monetary policy in a market economy. Because micro economic theories assume that there is no monetary policy in a market economy, they are considered the more simplified of these two economic theories.
Micro-economic models tend to be easier to come up with because there are fewer assumptions. They are also much easier to test and run, but they are more difficult to analyze using macro models because of the large degree of complexity involved.