The only reason to have lockouts is a lack of design initiative. That's it. The game has a monthly cost. They need to keep players subbed, which means spreading out the goal of that sub. In this case, its gearing through content.

This idea to prevent player burnout is false. Players will only ever play as much as they want to.

I've played MMOs that do not have daily, weekly, or monthly caps or lockouts on anything. When you max out one class, you merely start on another. New content is released around the time that the average player (if they start at day one) reaches most of their stuff capped, or even before.

The trick of course is to follow a very very simple design philosophy:

"When adding content or features to a game, would the players engage it without any reward?"

If the answer is yes, add the feature or content.
If the answer is no, redesign it.

If you're over 30, you'll likely remember when games did this. Many NES, SNES, Genesis (or earlier like Atari/Intellivision), and quarter sucking arcade games were like that. If you remember doing a play through of Super Mario Bros without using the warps in 1-2 and 4-2 to skip to 8-1 and instead played through Worlds 2, 3, 5, 6, and 7. There was no reward for doing so, just the experience of it.

This isn't to say rewards are bad. They should be tools. Like gear. Getting gear should mean opening up new content. Not opening content gets you new gear. Its a bit backwards.