There are at least two related reasons why the clearance rate for burglaries is relatively low.
First, the police tend not to have the resources needed to thoroughly investigate burglaries. These are crimes that do not result in physical harm to human victims. Therefore, the scarce resources available to police departments do not tend to get used on burglaries.
Relatedly, there is often very little evidence that can be found at a burglary scene. This is, in part, because police do not tend to devote a lot of resources to trying to find evidence. It is also the case, however, that there are usually no witnesses and very little in the way of physical evidence.
These two factors are important in making it very unlikely that any given burglary will be cleared.