Dear upjeet,
If TDS are deducted then you have to file your returns for interest received from the bank. So, the exchequer will get revenue. If it is not so many person who received the interest will not file their returns.So many people are filing their returns due to TDS, and they also show their other incomes also and pay taxes accordingly. So the main reason is to plug the revenue leakage, the provisions are there.Even some people never file their returns even after TDS. So those amount also goes to excehequer. The policy is to collect the tax , whenever the income arises.
regards