Actually the main reason for that was because the last three movies were made between 77' and 84', and while the effects were awesome, even for the time. When the first three movies came out much later with all the digital and CG effects it pretty much made it look like the technology level took an incredibly rapid decline.
I've always found it best, regardless of the era, to simply treat the tech level as a very fantastic thing and simply ignore the movies when it comes to those things, it'll only make your head hurt.
The hyperdrive has been around for at least 25,000 years, I treat the galaxy as a collective culture that has simply reached the pinnacle of what it can achieve, or wants to achieve, in terms of technology. The tech itself sees upgrades and new models, and a variety of improvements, but it never really advances anything beyond what they can already do.
That's one of the appeals of Star Wars for me, the blend of high and low tech into something believable. Take Tatooine for example, here we see a planet that is on the technological ass end of everything. No one comes here often and it relies mainly on what few traders stop by for any updates on what is recent news and state of the art. Most people on the planet are using blasters that are several models behind the curve, or that they've had to put together themselves. Same goes for speeders, tools, medical equipment, etc. I've always thought it awesome though that the people live in low tech Adobe style homes that appear primitive but are equipped with computers built into the doors and walls, etc. A perfect blend of low meets high tech.
It's best to just treat the galaxy as being filled with fantastic technology no matter which era you're in.
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It gets so lonely being evil.
What I'd do to see a smile,
Even for a little while.
And no one loves you when you're evil.
I'm lying through my teeth!
Your tears are all the company I need.