For a long time, that was the way it worked. Perhaps there was a policy justification for it at the time, but beginning in the mid-1970s, the Supreme Court and Congress have been pushing the law in the other direction. Most debatable constitutional questions in criminal cases today are far removed from the real Constitution and rarely have much to do with our confidence we have the right guy. On top of that, the asymmetric nature of habeas corpus make it a "heads I win, tails we take it over" form of review tilting in the defendant's favor, a tilt that is unnecessary and unjust when we are not talking about questions of actual innocence.
A big leap forward was made in 1996, when Congress enacted that a claim decided on the merits by the state court could not be the basis for a federal writ of habeas corpus unless the state decision "was contrary to, or involved an unreasonable application of, clearly established Federal law, as determined by the Supreme Court of the United States" or was "based on an unreasonable determination of the facts."
Defendant-leaning federal judges hate this law and have been evading it ever since. The Supreme Court smacks them down, sometimes harshly, but as one of the worst is rumored to have said, "they can't reverse them all."
Another smackdown came today. In addition to strong words, though, the Supreme Court closed a loophole, making an important advance for justice.