It would be fine if you could lock the locker, but since the management of lockers without locks are difficult, you can't leave your stuff behind.
ご質問ありがとうございます。
"It would be fine if you could lock the locker,"＝「ロッカーを施錠できるのならいい、」
"but since the management of lockers without locks are difficult,"＝「でも、鍵が付いていないロッカーの管理は難しいから」
"you can't leave your stuff behind."＝「ものを置いてかないで。」
ご参考までに。
Lockers with locks would be nice but it would be difficult to manage so no.
鍵付きロッカーならいいけど、管理が難しいからだめ。
- Lockers with locks would be nice but it would be difficult to manage so no.
- Lockers with locks would be nice, but no because they are difficult to manage.
「鍵付きロッカーならいいけど、鍵のないロッカーは管理が難しいから荷物を置いていったらだめ」
- Lockers with locks are fine, but if they don't have locks it is difficult to manage, so you are not allowed to leave your stuff behind.
アメリカ合衆国 
