MLG is very high wear and high maintenance equipment. So much so that many airlines have complete overhaul shops dedicated to just the gear.

Not only the movable pieces, but the trunnions take a beating as well. On an otherwise pristine appearing aircraft it is amazing to see how worn and beat up the gear can be.

Inspectors will quickly determine the cause.

Aircraft retirement
 

I guess this is one way to retire your old classics

They could have done it without pax on board

4 days ago in Peru:
2015-10-23 Peruvian Boeing 737-300 gear collapse at Cuzco » JACDEC


2 months ago in Indonesia:
Accident: Cardig B733 at Wamena on Aug 28th 2015, main gear collapse on landing short of runway


6 months ago in India:
Jet Airways plane's landing gear collapsed at airport in India | Daily Mail Online


last year, Solomon Islands:
Airwork (Toll) Boeing 737-300F right main gear collapses today in the Solomon Islands | World Airline News


etc....

Regarding the Cuzco Incident
 

"The aircraft was unable to taxi on under its own power.."

Given enough thrust I'm sure you could taxi, gear or not :-)

Accident: Cardig B733 at Wamena on Aug 28th 2015, main gear collapse on landing short of runway


The gear collapse in this one appears to be trunnion failure.

Yes, but the Cardig trunion failure was caused by the 3.68G landing which was in turn caused by not going around from an unstable approach.

I don't think that the problem is that the 737s landing gear is weak but the beatings they are occaisionally given in some parts of the world is immense.

Any aircraft's MLG will fail if you land hard enough on it.

Report released, flare started too high.
Accident: Comair B734 at Johannesburg on Oct 26th 2015, left main gear collapse on landing

Reading the report, the high flare was a contributing factor.
The root cause was an internal oil leak in the shimmy damper, after which the holes in the swiss cheese lined up. The MLG detached as designed to prevent wing penetration, spar damage and a serious consequent fire risk.

Full marks to all involved for the good outcome, it seems that trying to grease it on is a bad idea on the 737.

Full text here, including FDR readouts and Comair's response to the investigation report:

South African CAA - Aircraft Accident Report and Executive Summary

what sort of animals would be on a 737 , glad to see they were not injured.

Agreed. Here in the US, SWA and a few others and doing a MASSIVE amount of 73x landings every day. I'd imagine SWA is king of the cycles...

Gear seems to be staying on....

plainly not a wheel issue but rather a landing gear issue.