My bearers aren't tied down?

Two problems:
1. The flooring in my master bedroom at back of house is bouncy.
2. My room-width 3-door sliding wardrobe built directly against the floor/walls of another room gets jammed for months on end.

My house is 1970s cavity double brick on brick piers.

While crawling around subfloor of master b/r looking for cause of bounciness, I noticed that the bearers are bowing off the piers. I read in some other threads about tying down bearers to piers/stumps. Is there anything wrong with bearers not being tied down and not expecting any big winds?

The bowing is of concern in the room with the jamming wardrobe, because I think this explains the jamming. The bowing is more pronounced here - 3-4cm opposed to 1-2cm elsewhere - and explains why the jamming occurs only now and then. I used to think that the jamming was due to natural expansion/contraction from hot and cold weather. But there was a dry spell recently where the jamming disappeared (and we were able to access all areas of our wardrobe without engaging in contortionist manouvres, but this is another story); I'd have thought that the heat from the dry spell would cause the floor to expand. There doesn't seem to be a pattern to the jamming but I think I'll keep a log from now on.

This room is also the only one where we haven't put the final coats of polish on the floor - laziness has gotten in the way. We've only gotten as far as the Tung Oil seal. Could this be a contributing factor?

BTW, I'm hoping that replacing rotted joists in the Master fixes the bouncing, as mentioned in this thread https://www.woodworkforums.com/showthread.php?t=25937.

Thanks for your time and appreciate any suggestions.

I would reckon there would 1000's of homes around Australia that aren't tied to the piers and that not only includes brick houses.

I think you would find this came about after cyclone Tracey in Darwin and when they developed the Building Code of Australia.

Heat from a dry spell will cause timber to shrink.
Humidity will cause the timber to swell up and expand.

I'd be inclined to consider cutting selected bearers over the stumps so they settle onto the stumps and plating each side of the bearers with 100 x 38 kd hardwood. If you DIY don't forget to support the bearers while cutting so the house doesn't fall on you.

Its probably a job best left to a Carpenter/Builder as they may notice other factors that significantly affect the problem.

If the Piers are on clay footings the clay will shrink and leave a gap between bearer and pier. Just something to investigate.