Hello Shit Happens. There seems to be no reason whatsoever to make one's own irrigator if the one's supplied by manufacturers do the job adequately. However, in my case, the regular ones did not work for several reasons:
1) My peristomal hernia closed the hole just inside the stoma and the cone would not penetrate past it, so I needed a catheta arrangement.
2) I needed water pressure to assist the catheta to circumnavigate the hernia without causing damage. (the pump provided just enough water pressure to aid entry).
3) The water bag was insufficient for my needs ( partly because I had too much splashback without a cone ).
4) The only device which came somewhere near to my needs was the Braun irrigator ( I have written a review of this product and would not criticise it for performance apart from having insufficient water capacity and being far too expensive for my budget.) fortunately, it would have been available on the NHS except that it did not satisfy all my requirements.
I hope this answers your question as to why I have made my own device (s).
Of course there is another reason, which is that I actually enjoy experimenting to see if I can improve gadgets to help with the sometimes tedious processes of managing a stoma.