Why the ballance of the assets is always on debit side in T account?

Assets maintain a Debit balance and therefore any asset with a positive balance will be listed on the "debit" side of the account. The credit side of the T account for assets is used only to DECREASE that asset.

For example Cash is an asset account and it's balance is listed on the Debit side, now your company spends "x" amount of dollars, that entry will be listed on the Credit side to decrease the cash account. If at anytime your Debit side of the asset is less than your Credit side it means that you have a LOSS.

For example, you have $1,000 in your cash account and you record $1500 (credit) to the account. Your account will be listed as "OVERDRAWN" and will have a Credit Balance of $500, this of course is not acceptable.

A company can never have a higher Credit balance than a Debit balance in their assets.