The sequels treat Time Displacement as if it were easy

Skynet in The Terminator movie sent the original T-800 back in time, and after Skynet was destroyed, the Resistance sent back Kyle Reese to protect Sarah Connor, its target. Then in T2, the T-1000 was also sent back and a reprogrammed T-800 to protect John Connor.

But why didn't the Resistance send back a whole army of reprogrammed T-800s, and why could Skynet only send two terminators back? Probably because the Resistance were on the verge of shutting Skynet down, and it took a lot of resources to operate the newly-created Time Displacement equipment, and that even Skynet hesitated to send back the T-1000 through time, as a last-ditch gamble to defeat humanity once and for all, as it had no flesh whatsoever. But then Skynet was shut down, and it was left to the good guys sent into the past to defeat their enemies.

The TD equipment was new, uncertain, probably unpredictable, as the travellers ended up wherever and only whenever was certain, and must've caused massive power drains when it was used. There was also the issue of clearing up whatever was displaced when the subjects were sent through, because the matter in the displacement spheres was swapped.

So why would the franchise sequels continue to send more and more terminators into the past, with impunity, when Skynet had only just brought the TD equipment online, and that's what made the Resistance battle harder to break through to its core? Or did Skynet have the TD equipment operational for days? I thought the Terminator movie made it clear that Skynet had little time? Actually, I think I read that in the T2 novelisation.

The clear and concise story of the first two movies is undermined by the extra terminators sent back in T3 and Genisys and now Dark Fate, and it just makes it a muddled temporal mess. And I have NO idea about the Sarah Connor Chronicles, and how many goodies and baddies were sent back there!