1. There was a lot of exotic copy protection going on, especially on disk. Putting data in sectors that could not be written by the standard disk copying methods was just the beginning. I don’t know if any copy protection of tapes was ever effective but I wouldn’t be surprised.
2. To enable the use of “turbo” loaders. Cassette games were released on standard cassettes that were maybe shorter than normal. But if you compressed the games using better algorithms, you could fit up to 20 games on one side of a standard audio cassette. Normally the turbo loader was placed first on the cassette. It would maybe take a minute or two to load. Then, the rest of the pirated games followed. You’d write down the index number of each game on the cassette cover so you could fast-forward to it. The reason this was called “turbo” was presumably because as the game took up less space on the tape, you didn’t have to wait as long for it to roll past the read head. The c64 could decompress the data faster than the Datasette could play it back, so there was no processing wait. Most likely even a game that could be copied straight over to another cassette, still had copy protection that prevented it from loading using a different loader than it was mastered for. Hence it needed to be cracked.