A vast majority of success of Blitzkrieg hinged on surprise factor which was available only in the earlier stages of war:
Blitzkrieg, (German: “lightning war”) military tactic calculated to
create psychological shock and resultant disorganization in enemy
forces through the employment of surprise, speed, and superiority in
matériel or firepower.
Imagine that you neighbor a potentially hostile country. Imagine that country is getting its air force airborne in the thousands and preparing for an attack.
How are you going to know about it?
Spotter and recon aircraft cant just fly into that country's airspace without war being declared. Your spotters on the ground can only see what they can see with their eyes or binoculars. Interwar technologies like listening to aircraft sound only work when they are sufficiently close. You dont have radar, leave side a proper early warning system that works with the large radar network which you dont even have.
And enemy is amassing thousands of aircraft a few hundred kilometers from the border. Even if you somehow learn about it, how are you going to be sure if it is not large scale maneuvers as opposed to an actual surprise strike?
So even if a spy you have in that country reports you that something is happening, it is very difficult for you to actually act on that information because if you do mobilize your forces and attack your enemy, you would have started the war if the intelligence was wrong and they were not preparing.
That was the situation which faced USSR at the start of the war. They wanted to be prepared for the upcoming war, and to an extent they did prepare for it, but they didn't want to mobilize fully to risk giving Germany the opportunity to declare that Soviets were going to attack them and using it as a casus belli. And they would prefer to stay out of the war at least a few years more to prepare better.
What's worse, a lot of spies in Germany were informing Soviets about the impending attack, so they knew that an attack was coming. But the timing was a problem - previous reports were erroneous on attack date, and attack was postponed a few times. So Soviets expected an attack, but they expected it a few months to six months later.
So there you have the formula for success of Blitzkrieg
Germans come with thousands of planes, in formation, organized, with proper targets and objectives, what's more, with radios, just crossing the border in short notice, rushing towards Soviet airfields and aircraft which were just being alerted and scrambled. Even noticeable numbers of defending aircraft successfully take off, the disorganization would cripple their defense efforts.
There you go - if you catch your enemy on the ground or taking off, Blitzkrieg is easy. This is the way Germany was able to wipe out a lot of Soviet aircraft so easily.
Same thing happened in Battle of France despite France being on full alert and ready - it was just very difficult in early stages of war without radar networks and proper air defense coordination to fight against thousands of aircraft crossing your border - early in the war attacker had the advantage.
Same for Pearl Harbor - catch them on the ground, unawares.
But everything changed when Luftwaffe crossed the channel to attack Britain:
Not only Britain had extensive radar networks to cover the approach to the country, but also they had the advantage of having the channel and North Sea in between them and their enemy - which was already being watched by large numbers of observer aircraft just built for that purpose (like Avro Anson). So they were doubly prepared, so to speak.
All of that preparation was topped with a centralized air defense system which coordinated everything.
Results are well known - Blitzkrieg was suddenly not so blitzy anymore. Germans took some time to understand just how British were able to know when and from where they were attacking. A big change from the earlier surprise attacks they were so used to in early stages in the war. And they started bleeding aircraft and pilots like there was no tomorrow.
So to summarize:
Luftwaffe was able to repeat that feat by attacking unprepared enemies in repeated occasions.