Within the surrounding dialogues various parties (the Pharisees and Sadducees) try to entrap Jesus, but this skeptical scribe listens and affirms the truth when he hears it. We would expect the scribe to believe Jesus' answer to be a basically agreed upon interpretation of what is the greatest commandment, but we would not expect him to add in,
"...is much more than all whole burnt offerings and sacrifices.” (Mark
The scribe hasn't fully put together the fact that Jesus is the Messiah, the one bringing the kingdom and that he should abandon his own way and get on board with Jesus' way (repent), but he basically gets that it's not about the sacrifices and offerings. The scribe has the kingdom mindset, and so he's not far from the kingdom.
Edit to address Tau's comment.
There is a certain arc to the story of the Old Testament. The Hebrews enter into covenant with God, break the Law, then get new laws in response. The more history we get, the more we are shown Israel's failure to keep those laws. The Pharisee traditions, which the scribe would probably qualify under, attempted to address these issues by seriously doubling down to follow the law, and that involves a lot of judgement calls for edge cases and turning generalities into specifics. For example, what constitutes "rest" on the Sabbath?
However, a reader who meditates on the prophets, psalms, and wisdom literature gets a commentary on the Law that says that the legalistic rule following is an abomination to God when it is done outside of the pursuit of righteousness. Righteousness summarizing to the two greatest commandments. Because the whole world is the Lord's he does not need burnt offerings and sacrifices, but he wants people who love him, trust him, and love their neighbor. However, the people are hard-hearted. This is what the new covenant is meant to address: removal of the heart of stone and replacement with a heart of flesh.
Jesus' "kingdom way" involves gathering his people to give them the heart of flesh so that they can love God and neighbor from the heart. So when the scribe affirms the two greatest commandments in the context of a dismissing attitude towards the delight God has in sacrifices, Jesus affirms that he is really close to the kingdom.