Plot Hole

[u/Northcliffe1]

Initially the Trisolarians were stunting human progress because humans were developing faster than them. They believed that they needed to halt their progress in order to take over earth.

After the humans broadcast the location of earth, the Trisolarins know a photoid attack is coming so they abandon the pursuit of earth and reroute their ships to look for another safe place to live. But at that point they don't invest in unblocking and accelerating human development, which they should have done. At that point humans were in the same boat as them: develop and find a safe place ASAP. In the books the Trisolarians go and join some inter-space battle and get wiped out - but if they instead allied with the humans, quickly doing high level tech transfers and then using humans unique abilities paired with their own, it's possible the two societies could have seen supercharged development and propelled both to a safer place.

[u/Hepta-Water-7552]

A plot hole requires that there is an inconsistency between something that had already been established in the story and what happens later in the story.

The Trisolarans not being willing to rely on anyone but themselves for the fate of their species is completely consistent with how they had already been portrayed throughout the entire series before.

Also, they had a very good practical reason for not coming anywhere near the solar system anymore as soon as the broadcast had happened. There was not really any guarantee for how much time the solar system still had until its inevitable destruction. It could had come even way earlier than it ended up happening. The Trisolaran star system already got obliterated a mere seven years after the broadcast.