Why do real estate agents advice to lower selling price?

I will assume you mean "advise".

There are multiple potential reasons. Here are a few possibilities in no particular order:

1. They do not think the property is worth the asking price.

2. They want to sell it quickly.

3. The market may have told them the price is so high buyers won't waste their time making an offer.

4. They have invested too much time on the property and want to get rid of it.

5. They believe they can start a bidding war.

6. A reduction may be part of a larger marketing plan.

7. They do not know what the property is worth.

8. A potential buyer has suggested they will make an offer if the asking price is reduced by X dollars.

9. Price overcomes ALL objections.