qBittorrent official forums

To avoid the hustle of always re-tick the "Download in sequential order" box i would suggest an option in qbittorrent settings to always leave it as "true". Or even better an option so that qbittorrent "remembers" the modifiers you last chose when adding a new torrent.

I'm suspect it's deliberate. There are some scenarios where it would be very bad for the torrent if most of the downloaders did this.