It seems like they're trying to remove really low frequencies, but does it really make that much of a difference? Is there a particular reason why this is done?
The practical reason is going to be due to the instrumentation between the transducer and the software processing the information. As a practical matter it is difficult to remove all DC offsets in the electronics. (IE, it costs money with extras parts or calibration procedures). If the signal has no meaning at DC, it is much cheaper to not spend as much removing all of the DC signal in the electronics, and instead remove it in the signal processing.
As a practical matter, actual systems are rife with parasitics. Things we do not understand or do not want to bother to control for. Since it is almost as easy to implement a band pass as a low pass, and there is no useful information at these low frequencies, it is good design practice to filter the data, so that design parasitics in those frequency ranges do not need to be otherwise dealt with.
What does it mean to block DC?
DC is going to appear in the data as an offset. This can cause various design headaches. One is scaling. A significant offset can cause data to saturate in various processing stages. It may therefore be necessary to increase the dynamic range of the processing stages to deal with large DC (offset) components. And if these signals are not useful, then removing them can make things easier.