This is actually a policy that has come about for several reasons. Mainly:
1. Custom avatars have from the beginning of Buffy-Boards been a "perk" for the board moderators. They are not paid for the work they do or the time they spend helping out, so this is one of the few rewards we can give them.
2. Custom avatars eat up bandwith. This is a very bandwith intensive site. Allowing our members to have custom avatars would dramatically increase the amount we use each month, which increases the amount we have to pay to keep the board running. Custom avatars also increase the time it takes to load a page, making the boards run slower.
3. Other boards we have been associated with over the years have tried allowing custom avatars, only to find out that it doesn't work and going back to not allowing them. We have learned from their mistakes.
4. We want to be able to control the quality, loading time, and content of avatars on the site. It would be too difficult in a board of this size to do this on a member by member basis.
5. Having had our avatars stolen by many many other boards over the years, out of respect for our fellow administrators we don't want to have our members taking other boards' avatars without permission (which inevitably would occur unfortunately).
6. We like to keep custom avatars as something we can use to reward members for winning contests etc.
7. We like making avatars.
8. We offer a large assortment of avatars and don't feel that custom avatars are necessary.