To face the scaling problem, why don't we decrease overall difficulty to generate blocks more often?
Theoretically, the new block of Bitcoin should be added every 10 minutes. If the miners will add blocks more often, the current difficulty will be re-calculated and, of course, be increased.
In this state yes but with an update to the bitcoin core?
In other terms, why we don't reduce the block generation time to reduce the scaling problem?
It would require a hard fork which means that every single Bitcoin Core version before the fork cannot be used anymore and its obviously a problem.
If you're going to increase the block interval, you will be having the same effect as Bitcoin Cash, which increases the block size. This doesn't solve the problem with the storage and bandwidth issue but it would just introduce another problem with the hard fork.