Making the loot stored in tne th larger will make more keep the th in. This will add more bases to loot and less next because small bases cant snipe to where they don't belong
Sitting th outside, getting free shields also keeps th 10s who sit down low to take easy loot. Why reward them. If you take away shield for th then do raids based on same as war search. Nothing worse than full storages on a th 8 sitting in gold 3 getting wiped by a max th 10 with no prayer of a revenge.
TH sniping is an important part of the COC ecosystem and economy. It's a great example of symbiotic cooperation between groups with differing goals. Take it away and folks will just find alternate ways to protect their stuff. If you want people to keep their storages full for you to raid, then find a way to reward that behavior.