Parshat Shlach: Getting punished for doing Tshuvah?

Why were the people who wanted to make up for the sin of the Spies punished when they tried to enter Israel?

Tuvia and Yitzi ,

Talking Parsha
Talking Parsha
Tuvia and Yitzi

Why were they punished for doing Tshuvah??

This week we read about the Ma'apilim מעפילים.

The group of people who when recognizing the sin they had done of not wanting to enter Eretz Yisrael, decide to change their mind and get up and make there way over to the land.

As we know, this was a bad idea and failed miserably.

This raises a big question - why was this such a bad thing to do? The Torah testifies that they regretted their ways, they seem to have done Tshuva, and now want to correct their mistakes and go without fear into Eretz Yisrael. What's so bad about that??