I’ve seen “forgotten wells”and missing sump pumps many times while inspecting remodeled homes. There could be many different reasons behind it:
they simply forgot to install a sump pump
new drain tile was installed and connected directly to an exterior, updated drainage system with no need for a sump pump
new drain tile installed and the sump pump relocated to an exterior well
lack of communication between the developer, contractors, laborers… maybe it wasn’t supposed to be there, somebody just assumed sump pump installation necessary but in the process changed its mind…
Talk to the neighbors about it, look for any discharge pipes on exterior… if you have no flood problems in the area there might be no need for a sump pump at all.