There's a lot of good discussion on this sub about why Market Garden failed* and what would have been the consequence if it succeeded. To me, the more interesting question is;
Why didn't the failure of MARKET GARDEN matter?
In multiple times, the Germans proved incapable of turning tactical or operational victories into strategic success. Was there a significant reason for that? Bureaucratic infighting? Unfamiliarity with proper defense strategies? Poor decision-making? Could the Germans have turned the failure there into a proper routing of the Allies?
* Principle reasons for failure tend to be overextension of supply lines, lack of fuel, and loss of flank guards - all stemming from over-ambitious speed of advance. I would argue that Marshall's plan was tactically sound (use of surprise & mass), but operationally flawed (aforementioned supply lines, not knowing terrain, and the op pause at Antwerp) and an error in strategy (didn't achieve end-goal of route over Rhine; ended up with British relegated to backseats of planning for rest of campaign). Just saying - I have done a little reading. Thanks.
The problem for the Germans, even after the failure of Market Garden, was that the Allies were stronger. The Allies had begun the battle stronger than the Germans, and the Germans took higher casualties, perhaps up to double those of the Allies. The number of Germans captured was about the same as the total Allied casualties, and while the German killed and wounded total (not reliably known) was probably lower than the Allied killed and wounded, it might not have been much lower.
What had the Allies achieved during Market Garden? While they had failed to capture the bridge over the Lower Rhine at Arnhem, they had captured the bridge over the Waal at Nijmegen, and held a substantial bridgehead between the two distributaries of the Rhine (upstream from Nijmegen and Arnhem, the Rhine divides into the Waal, bridged at Nijmegen, and the Lower Rhine, bridged at Arnhem - the Allies were halfway across).
What could the Germans try to do? They could try to pinch off the Nijmegen salient at the base. They were too weak to be able to make a serious attempt. They could try to destroy the bridge at Nijmegen. They tried and failed. An attack by frogmen a week after the end of Market Garden caused some damage, but failed to destroy it. Later attempts were made by floating mines done the Waal and by attacking with midget submarines. Both failed. They could try to capture the bridge, or at least eliminated the bridgehead over the Waal. They tried and failed - the German forces in the area were too weak.
The only realistic chance for the Germans to achieve anything would have required strong reinforcement. Available forces and supplies were being readied for the Ardennes Offensive, so such strong reinforcements weren't available. The best the Germans could have done was to bring in more forces to fight for the bridgehead, which would have brought in more Allied forces, and produced a brutal battle of attrition with the Allies on the defensive. This would have favoured the Allies, and bled the Germans for little or no gain.
Fundamentally, this is often a problem with a defensive victory against a stronger enemy. You stop them, but are too weak to take the initiative. The enemy tries again, and at best you win another defensive victory, and it continues. The Ardennes Offensive was an attempt to break this cycle, and in the event the Germans were too weak to have a realistic chance of success.