Confused about seller's concession

[Salma M.]

So I finally found a property I want to invest in. I made an offer of USD 600k purchase price+20k seller concession. I am preapproved specifically for this. The seller is not happy about the seller concession. I don't understand why. My mortgage amount goes up because of the seller concession. I am bringing to the table 20% downpayment (USD 124k). Why would he not want to take it. My offer is also the best he has received to date!

So two questions. Why would a seller say no to seller concession when he doesn't have to pay for it? Do I wait for him think this through or take my offer off the table? Basically how long should I give him to decide?

Thanks in advance for the advice.