Because they can afford an Anaconda?
I like the idea of a range of dedicated exploration ships, and I would consider the ultimate to be very similar to the Anaconda in size, but with a more open bridge and higher class FSD or lower weight, and better SC handling. The net would be able the same range as now, but weight lost from shedding hard points, power distributer, and thrusters would be replaced with weight from additional, SRVs, SLFs, minining laser + refinery, limpets, and other non-combat or hauling equipment. While this is essentially what is being done today, even with lightweight mods, G5 FSD, no hardpoints and no shields, adding much more than the SRV, SLF, and AFMU will significantly impact the max jump range. Again, not essential to exploration but are a big deal when its time to come back home.
Give me an Anaconda with a Beluga's bridge, Sidewinder's hard points, DBx SC handling, minimal shield capacity, 65ly jump range, seven internal slots, minimal power plant, minimal thrusters (no need to boost or go over 200km/s), and maybe some advanced scanners that would be useless in any other ship. And let the SLF and SRV only be compatible with exploration variants, which also have better scanners and recon abilities.
This class of ship would be worthless for combat or trading and only marginally effective for general mission running.
And it should be big. Big enough that upon seeing one depart from a station, one pause and wonder at the far off places that ship must be setting out for.