As this is a very basic question: If you’re new to SAR I recommend the SAR EDU page which provides lots of information about the SAR principles and theories as well as tutorials and talks: https://saredu.dlr.de/
The visual amount of information is related to the distribution of backscatter information over the given color range: While the VH intensities have an extensive range and only very light objects appear sharp, the db data is logarithmised, meaning that the values are now distributed more evenly over your black/white color range. This leads to a higher presence of grey pixels and less extreme values.
HV (non logarithmised)
HV db (logarithmised)
note how the total range of the image above is nearly 2000 (0 to 2000) units while in the image below the colors are distributed more evenly over about 50 units (db in this case, -40 to +10)