I didnt ask why and TBH length of service has sweet FA to do with a player being club captain!
For me what has shone through and is also likely to be apparent to AVB and may influence his selection of Dawson is his leadership qualities lead by example, never give up, loyal to the club, the cause, fully committed and reliable.
Yes there are better players technically in the team/squad even at CB such as JVT and Kaboul (barring injuries) but they lack those extra qualities that Dawson brings to the field he is a true THFC player through and through and that is a great example to others and his passion for the club also!
Thats my opinion why he is captain!