Of course, this also includes a contract extension and a significant salary increase and that is why he chose to stay at Leipzig. Benjamin Šeško is still very young at 21 years old so a talent like him will be very valuable for Leipzig in the future and his market value could increase with the quality he continues to improve every season.
Source: https://twitter.com/FabrizioRomano/status/1800443297443570011
Leipzig is one of the rich teams of the Bundesliga. I don't know whether they are as rich as Bayern Munich but it is still enough to sign really talented players. However I must admit that I wasn't expecting Sesko to stay. After having quite productive seasons two times in a row, I thought there would be some big teams after him this summer.
Leipzig are regularly qualifying for the Champions League so this must also have some effect. Another thing might be that Sesko wants to be at a team to play regularly. Besides Leipzig must also be satisfying his demands in salary as you mentioned.