I guess it was still the time when good recording did cost money. These days you get a semi-professional recording studio in the shape of a laptop including a sequencer and a reasonable good mic for less than 3000 Euros and when you pay for mastering, you'll likely get a sound no pink floyd would have been able to create even with unlimited studio time. At that time every pound invested had a direct connection to the sound in the end. Especially drums aren't the easiest thing to record, especially when jamming together with other musicians and when studio time is limited due to having some special deal (I think it was Queen who were allowed to use a studio while it wasn't booked, which kind of explains their rather good sound on Queen I compared to slightly older recordings like Mad The Swine).
So I'd guess, its just a low budget production and they did what was possible.
Among all these wolves...