Your lack of flexibility
stops you from progressing and using certain parts of your jiu-jitsu game.
Yes we are all different shapes and sizes and because of that we all create different angles and movements but don't you want to unlock the potential to create as many different shapes and sizes as possible?
Working on your flexibility will give you the ability to add a whole new arsenal of techniques that you were unable to do before. You will have a wider choice of options from positions because you have more movement in them than you had before. With more options you will be able to stretch further, reach higher and because of that you will find new openings to escape or progress.
Opening up more angles could improve things like your guard game and make you that small percentage more impossible to pass. How many times has someone been working a pass and only succeeded by that tiny bit?
Now imagine if you had worked on your flexibility and gone back to that pass, things could have been different right?
Working on your flexibility will allow you to create even more of those angles and movements that you created before, the more options you have available in a position the more opportunities you have in that position and your jiu jitsu game can only improve from that.
Give yourself those options and opportunities.