There are several reasons that manufacturers make sealed cans you can't take apart:
1) A sealed can is generally cheaper to make
2) A sealed can is generally quieter
3) A sealed can is generally lighter
4) You don't really need to to take apart some cans: center-fire rifle cans, for example. Or even center-fire pistol cans, providing you're not shooting really dirty or non-jacketed lead ammo through it (though I prefer serviceable pistol cans).
The main ones than actually NEED to be taken apart are .22 cans, and if you notice the trend in the market is for serviceable .22 cans; there are very few sealed .22 cans on the market these days.
0331: "Accuracy by volume."