The crowd loved Jesus, but their desire for Him reveals a fundamental misunderstanding of His mission.
The people "sought him, and came to him, and would have kept him from leaving them." Their eagerness to keep Him with them stemmed from their immediate needs and desires. They had experienced His power to heal and teach, and they wanted more of that relief and provision for themselves. As one commentator notes, they wanted Him for "miracles, the healing of their sick, dispossessing demoniacs, &c."
However, Jesus' mission was far greater than just addressing immediate physical needs. He states in the parallel passage in Mark, "I must preach the gospel of the kingdom to the other cities as well; for I was sent for this purpose" (Mark 1:38). The people were focused on the present benefits, while Jesus was focused on the purpose for which He was sent. Their desire to 'keep Him' was, in essence, to domesticate Him, to limit His ministry to their local needs, rather than understanding His global mission to preach the good news to all.