Why have these interesting devices fallen out of favour on buses and trucks in the last two decades? Some private bus companies fitted them as standard (Eg: North & Western Bus Lines) some that didn't at all(Eg: Harris Park Transport Co.) and some who fitted them on some of their buses (Eg: Deanes Coaches/ SouthTrans).
Truck trailers still commonly use them as that is the only means of measuring their distance accurately, but why have they stopped fitting them on the vehicles themselves? They look good and it's another aspect to buses and trucks that has served to make them blander than ever. Even the STA fitted them at one stage during the early 1990s.

They look ridiculous, are outdated and unnecessary?

Daniel wrote:They look ridiculous, are outdated and unnecessary?

But are part of bus history and look cool to me. You know what they say about opinions.

In this era of computerised record keeping they would serve no purpose, all readings can be taken from the odometer.

Computers fail and fail often. Hubbos rarely do.
Here is one I took today on Sydney Bus Museum Atlantean decker 1003. It has been on there for over two decades and just keeps on recording, yellowed lense and all.

Visitors to Darwin will note a number of the earlier O500LE's are fitted with Hubodometers. Can't remember specifically if the B10s, B12 or Scanias had them.

Many are now using engine hours as opposed to kilometre based service scheduling

Engler made hour meters too.

Well, it looks like the contractor for Randwick council garbage trucks favour the use of them. I saw one mounted on a late model Volvo garbage compactor and also noticed one on a Mercedes a few weeks back.
I also saw one on a Melbourne fire truck on the news recently.
They all were like this one.