> They don't need to be doing either serious or competitive sport to want all the paraphenalia. Think of all the Weekend Wigginses, with their shiney shorts, branded water bottles, £800 bikes, insect-like cycling goggles, top of the range Go pro, and all of this topped by some form of tracking system, so that they can drone on to similarly minded people. It's the same with the faux Farrahs, and outside of sport, we do it too. Amateur photographers with thousands of pounds of kit, when they never take a single interersting photo. DIY'ers with every tool known to man.
Most of what you've listed are pieces of equipment that, while the quality/cost/specifications may have exceeded the requirements of the activity, are in general needed for that activity.
> shiney shorts
If you are going to go running you probably want to do it in a pair of shorts, good running shorts provide support for the old fella to stop chafing. So a pair of good quality running shorts for any regular running is important. Sure, getting gee-whiz 'shiney' shorts might be excessive, but it is spening more money on something that is needed anyway.
> branded water bottles
Again, having sufficient water when during exercise is important to prevent stitches and dehydration. Sport bottles are designed for a purpose - being able to drink from while still on the move, easy to hold/attach and so on. So a water bottle is important if not a necessity, and again going for shiny/bling whatever is merely spending more on an item that you need.
> £800 bikes
If you are going to go bike riding you sorta need a bike. Like anything, if you can afford a 'better' one than the base model you need, what else are you going to spend your money on? There is only so much money you can spend an the absolute base models of everything, if you have extra money burning a hole in your pocket, why not go for the better spec'ed/quality/blingy/'cool' bike?
The same for pretty much everything else you've mentioned. Pretty much all of it is necessary kit, bikes, cameras, whatever - for the activity chosen, however people go overboard (or like to believe they are skilled enough - or will get skilled enough - to need the extra features) and spend more on 'better' equipment than they need.
And yes, there is an element of one-upping or specification/checklist comparison of items to make you feel cooler/superior to others, etc.
But, none of that is true for fitness trackers.
You don't need to count your steps.
Or measure the distance precisely.
Or calculate the calories burnt.
Do exercise until you've felt you've done enough. If you are still gaining weight (for example), then you have to do more. You don't need anything more than a glance at the clock before you start your exercise, then glance at it when you've finished, or how you feel after the exercise, to know how much you've done or whether you ned to do more or less.
Of course, if you feel the need to absolutely quantify the effort for some reason - bragging rights - then knock yourself out on getting a fitness tracker. But don't fool yourself into thinking it's in any way necessary, unlike most of the other items you listed.