You know there were only three (maybe four) SSDs made, right? 
Do you have a source for this? The Empire could build a thousand SSDs if they wanted to. Hell, a Death Star is easily worth tens of thousands of SSDs.
First, check out
http://www.starwars.wikia.com and search "Super Star Destroyer."
Second, sure the Empire
COULD have built thousands of SSDs
if it had lasted as long as the Old Republic, but the Empire had only existed for about
twenty years (20) by the time they finally developed the Lusankya/Executor.
Third, SSDs require
SO MANY RESOURCES that they'd have to go intergalaxy to find enough resources.
Fourth, SSDs cannot, I repeat,
CANNOT turn on a dime. One of the contributing factors to the end of the Executor was the mere fact that the secondary bridge couldn't take it out of the dive.
Fifth, just after Princess Leia became Chief of State, the New Republic had an easy time keeping the Empire in check. Why? (those of you who've read the Thrawn trilogy know this) Because all of the experienced officers died on the Executor, leaving the Empire in the hands of newly trained cadets.
Sixth, you don't
need an SSD to keep citizens in check. Look what Grand Admiral Thrawn did with his, what,
three ImpStar Dueces (Imperial Star Destroyer Mark II). As, major shift here, Colonel O'Neill said,
This (Both an SSD and the Death Stars) is a weapon of terror; it is meant to
intimidate your enemy.
This (An Imperial Star Destroyer, any class) is a weapon of war; it is meant to
kill your enemy."
Point taken?
Edit: IIRC Tempest, the bridge needs to sit much further aft.
