Why Gas cylinders should be kept in sun shade?

I read in Rules for gas cylinders that gas cylinders should be kept under sun shade, should not be exposed to direct sun light, the storage area should have good ventilation, etc. Though the reasons are known, i.e to avoid over pressurization due to the exposure to sun, I saw practically how over pressurization takes place in the cylinder when exposed to sun light directly.

Recently, I was on a visit to one of our sites under construction. After my visit to the construction site, at about 1230 hrs in the noon, I was going back to the office where I normally sit. I don't have permanent table and chair as I visit the site occasionally and there are permanent safety officers already appointed at site. On the way, I saw some argon cylinders stored on the road side under direct sun light, without valve caps. I enquired with the contractor nearby about the cylinders and I was told that they are empty and are to be sent to the supplier. On close observation, I found that the valve discharge nozzle is having some water (there was rain on previous night) and small bubbles were being formed continuously.

From this I understood that though the cylinder is empty, it is not 100% empty and some leftover gas in the cylinder is getting expanded due to rise in ambient temperature. As the valve is not totally closed, the expanded gas is leaking out as bubbles through the water in the discharge nozzle.

This clearly demonstrates that though we assume empty cylinders are safe, they are not actually 100% empty and if the gas is toxic, then the little amount of gas leaking out due to sunlight exposure can harm the persons nearby. If the cylinders are full then they are hazardous and can endanger the persons around.

Similarly, being found on the roadside, any damage to the valve (breakage) can rocket the cylinder like missile and can hurt persons / damage equipment or property nearby or can have a domino effect. For this reason, the rules are specific that the unused cylinder valves should be protected with valve caps so that valves can't be exposed directly.

People talk about safety culture so much, but these small issues like valve caps, cylinder storage under sunshade, chaining the cylinders to prevent their fall, etc are not given due attention. Lip service alone will not improve safety culture. May be, talking about safety will bring admiration from listeners and even some appreciation by way of reward, but this will not help in improving the safety at ground level and all this admiration / appreciation / rewards will be washed off by any single accident and the same persons will admonish the in-charges of the area for not visualizing the hazards and not taking corrective measures for the safety of the people.