It's competitive for the people who want it to be, as they can look up their times afterwards (and for the best ones, see where they finished), compare themselves to others of similar age to see how they are doing relatively (as no 60+ is likely to want to compare themselves to 20somethings), and see whether they are improving relative to others. This can be a big motivator, even for those of us who will never be at the front - I'm a pretty terrible runner, but would still feel chuffed to move from e.g. lower half to top half of my age group.
Anyone who isn't interested in that aspect is free to ignore it, and clearly many people are not interested, and are just happy to finish, stroll round with their buggies or whatever. They are under no obligation to look at the times and stats afterwards, and are welcome to blissfully ignore them - so they are unaffected either way.
However, currently, for the people who DO value the competitive and/or performance-rating elements (and there are many, as the complaints over dropping the results previously showed!), there is currently a big bias, as male runners a) are much less likely to have their results/performance ratings affected by people running in a "gender" category that doesn't match their sex (and if they are affected, the difference is likely to be much smaller, and usually in their favour), and b) they have the option to massively increase their performance stats, at the expense of female runners, if they choose to run as a "woman".
Whereas women do not have that option to artificially bump up our own stats, and we DO stand to lose out much more when other people do, including potentially losing first position or other top positions in our age categories, and even overall first female finisher positions for the best women, to men - but it also affects every single woman lower down the rankings too.
HOW exactly is that fair, or "inclusive", to women? It would be easy enough to include both sex and "gender" if they really wanted, but even just listening to women and showing some understanding of our disappointment would be a start. Instead, Parkrun have been quite insultingly dismissive of women who complained, while (it seems) bending over backwards to let a small group of men get what they want. The misogyny and hypocrisy seems even clearer when you realise that a lot of the men prating at and insulting women online the most about this are the exact same men who ARE quite competitive themselves and were e.g. in groups tracking who had most "first finishes" and so on, but then love to tell women they should F off because "it's non-competitive and inclusive blah blah" (thinking of some of the ones I've had run-ins with previously!).