1. Supply is not ready to push prices lower.
2. People are taking gains from the top of the resistance area (don't want to push market lower by overflooding supply?)
3. People are entering short positions near the top, and not willing to add short positions at the bottom of the resistance (don't want to push market lower by overflooding supply either?)
From the short POV, entering shorts or selling long at top of the market, but not willing to flood the market yet to maintain higher prices when entering short or offloading long positions
Reason for low vol on the bottom of the range can be, there is not a lot of supply near the bottom and bulls are quickly eating up supply at the bottom of the range, thus more volume at the higher end of the range. Obviously if there is a lot of people willing to buy, shorts don't want to offload at lower prices.
However, bulls are not willing to push the prices higher at the last hour.