An Explorer ship would be expected to at least bring back a few samples, why doesn't the Terrapin have at least that?

Finding samples on trips, recovering some salvage, that's all something that can be placed inside the Terrapin and brought back for the eggheads to study or someone to make a buck on the black-markets of GrimHex, but the Terrapin's focus is on data collection, worth its SCU weight in gold. Selling the mining spot on a virgin world or finding the location of the most wanted pirate lord in 3 systems is what the Terrapin pilots are all about, and those are the paydays they are chasing. If bringing back cargo and salvage from these trips is something you're more interested in, as I talked about the scale of explorers, it may be that buyers want a ship more suited towards that, but there will be a payoff of more cargo space meaning the ship loses scanning and radar abilities as a result.