BuildCraft version: 7.99.15-pre4
Forge version: 14.23.1.2555

The reason is unknown.

this has been mentioned before in chat, dug up the screenshot:
https://cdn.discordapp.com/attachments/401767220755300362/402945125304762369/image.png

It was actually 3 different problems:

1. ChunkLoaderManager was requesting too many tickets.
2. Quarry wasn't providing correct chunk list. It has been missing some:
   • Ones around corners, as it was using wrong comparing operator (strictly less instead of less).
   • Ones that are only contain blocks from frame box, not from mining box.
3. BuildCraft had maximum of only 25 chunks per ticket, instead of 26 that quarry might need (1 chunk for quarry itself and 5 * 5 chunks square for working area).