Why does the narrator considers a tow-line to be nuisance?

The narrator is certain that tow-lines minds of their own.

There is something very strange and unaccountable about a tow-line.  You roll it up with as much patience and care as you would take to fold up a new pair of trousers, and five minutes afterwards, when you pick it up, it is one ghastly, soul-revolting tangle.

I do not wish to be insulting, but I firmly believe that if you took an average tow-line, and stretched it out straight across the middle of a field, and then turned your back on it for thirty seconds, that, when you looked round again, you would find that it had got itself altogether in a heap in the middle of the field, and had twisted itself up, and tied itself into knots, and lost its two ends, and become all loops; and it would take you a good half-hour, sitting down there on the grass and swearing all the while, to disentangle it again.

That is my opinion of tow-lines in general.  Of course, there may be honourable exceptions; I do not say that there are not.  There may be tow-lines that are a credit to their profession—conscientious, respectable tow-lines—tow-lines that do not imagine they are crochet-work, and try to knit themselves up into antimacassars the instant they are left to themselves.  I say there may be such tow-lines; I sincerely hope there are.  But I have not met with them.

The narrator considers towlines to be a nuisance. There is something very strange and unaccountable about towlines. One rolls it with as much patience as possible, and afterwards it gets entangled in itself.

Infact, Jerome even believes that if one took an average towline, and stretched it out across the middle of the field, then turned back for 30 seconds, and looked round again, he would find that it has become a heap in the middle of the field. And,it would take you half and hour to disentangle it