Various commentators address this question, in one of two ways. Either Caleb did do something better than Joshua (1), or that Joshua is not mentioned for some reason here (2). I have focused on the (classic) Jewish commentaries, which can be found in Hebrew at this link.
Approach 1 - Caleb conducted himself better than Joshua in some way:
Ibn Ezra points to Numbers 13:30 as the answer to this question, saying that the reward came for Caleb's silencing of the nation, and stating his confidence that the nation would be able to conquer the promised land.
Luzzatto, Berlin and others note the opinion of Rashi (and others) in Numbers 13:22 (the translations ignore the singular verb; see Ellicott and Gill at that link) that Caleb was the only spy that entered Hebron, which was particularly dangerous, and therefore, he was rewarded by receiving that piece of land.
Approach 2 - Joshua is not mentioned here for some other reason:
Hizkuni says that since Joshua was the one leading the nation into the promised land, it did not need to mention that he would be entering it, however, since Caleb was not (such) a major character in the entering and conquering of the land, it was necessary to mention here that he would also be entering the land.
Hizkuni suggests that alternatively, the main reward was that Caleb's descendants would take possession of Hebron, and since Joshua did not have children, he was not included here.
Nahmanides suggests that Joshua's reward was the leading of the people into the promised land, and that the place for that is "elsewhere" in the Pentateuch, as it would be inappropriate to tell Joshua that he would be leading the nation into the land while Moses was still the leader.
(An additional factor to consider is that Joshua was already known as Moses' assistant, but I'll leave the answer as is for now.)