When their finances are in dire straits, Barcelona must prevent a frantic transfer. It would be much better for Barcelona wait one more season until his contract runs out at Bayern Munich than to have to spend a lot of money on a player who is 33 years old. Lewandowski's golden age as a footballer is over, although his performances last season with Bayern Munich were very good, there is no guarantee that he will be able to maintain his form for another 3 years. The age factor can affect a player's appearance, both in terms of strength and sharpness on the field.
The best solution for Barcelona is to wait until Lewandowski's contract runs out, they can sign him without spending a penny.
If Barcelona waits for Lewandowski's contract period to expire at Bayern Munich with Lewandowski's age going to 34 years, then nothing good can be obtained by Barcelona through Lewandowski, so Barcelona will also be in vain if they have to wait for Lewandowski to end his contract. Since Barcelona in general are in need of some great players to stay competitive in the Premier League as well as in the Champions League, one of the options is Lewandowski.