for the longest time inventories have been stored client-side on bds which is appalling for server owners making it so people can give themselves items that shouldn't even exist such as weapons with 32k enchantment values and even objects that allow CBEs[command block exploits] crippling servers making them unplayable, this is even an issue on the PAID realms service
owners having to resort to systems like Nukkitx or cloudburst which have allot more weight than bds while being more limited missing items and features