They look shocking on the face of it but relative to other clubs at the time and considering we spent 4 out of 10 seasons in the 2nd division during the 1980's, our crowds held up really well.
I don't have the exact figures to hand but as far as league games go, out of all the clubs in England we had the 3rd highest "lowest" league crowd during the 80's. Only United and Liverpool bettered us. United got 23k+ vs Wimbledon, and Liverpool 17k+ against someone who I can't remember. Our lowest league crowd that decade was 15k+ vs Reading and Millwall.
For comparison, Everton dropped to around 13k when they wanted Kendall out, Arsenal got 13k for one game in about 1983 when they were something like 3rd in the league, Spurs dropped below 10k at the back end of the 85-86 season, Chelsea dropped below 10k at various points (as they did in the 90's too), and I think Newcastle flirted with going below 5 figures as well. So 3 of the so-called Big Five at the time recorded lower league crowds than City during the 80's, despite being top-flight ever-presents throughout the decade whereas we went through 2 relegations.