[NeedMoreTea]

There is a very important difference. The normal conference season is just a break, a holiday. Any debates, work or legislation continues where they left off after they get back. If something important happens, they can and have come back early or might vote not to break. The runes were showing that a long break would have been trimmed by parliament.

Proroguing parliament ends the parliamentary session. Any work in progress, debates on bills and what not are cancelled as void. A new session of parliament starts from day one on everything, with a Queen's speech, State Opening and what not. That's why toward the end of the parliamentary year there is often a rush to get matters concluded and bills enacted before prorogation. Coming back early is much more difficult.

This move effectively turns the whole parliament into a one issue organisation and disables debate.

https://www.parliament.uk/about/how/occasions/prorogation/