Traxcavator -
1. Has much better "grip on the ground", and much better digging ability than any wheel loader.
2. Has tracked undercarriage which is "spendy" compared to tires, when they're worn out.
3. Doesn't get flat tires or blowouts.
4. Because it has tracks, it's slow over the ground. Any distance to travel, and the wheel loader runs rings around it.
5. Because traxcavators have fixed (bolted, non-articulating) track frames, they ride rough. You need a good suspension seat on them.
6. Thanks to the fixed track frames, traxcavators are more stable when you have a full bucket raised and you're moving with it raised.
7. Need a lowbed to move them around.
Wheel loader -
1. Hasn't got the traction of a tracked machine. Spins tires in poor underfoot conditions. So you need to keep good conditions underfoot.
2. Has tires that are much cheaper to replace and repair - but be prepared to fix flats a few times a year if you work in sharp rock, or where there's metal trash in the ground.
3. Is fast over the ground and they're great for "tramming" materials over a considerable distance. This really speeds up production.
4. Wheel loaders give a better operator ride than traxcavators.
5. Are not as stable when moving with a full bucket raised. Drop into an unseen pothole or have the ground collapse under weight application with the bucket raised, and you are likely to roll over. Add in, turning when bucket raised, and stability gets worse again.
6. Can "road" them from place to place if not overwidth for roads.
Traxcavators have fallen away in popularity over the decades, basically because tires have got better and bigger and more robust for most wheel loaders, and undercarriage costs have outpaced tire replacement costs.