Recently my tomato garden has been plagued by this, I don't know whether is it pests or a disease. Once the first signs starts showing up, they can die within a couple of weeks. Anyone known what this is? I appreciate your response.

Are the leaves browning and shriveling or are large pieces missing? If it is browningvand rolling, some kind of spray hit them? Or if pieces of leaves are missing, do your plants have caterpillars eating them? I can't tell for sure.

Upon closer inspection of the severe damage, I would say chewing insects are eating the leaves.

Some of the dead leaves have been trimmed off, the leaves have this dry light brown spots that does roll.
I only been spraying them with insecticides. I thought maybe it's something eating at the roots because I can't see any caterpillars.

Root damage would not cause that, an overall wilting but not that.
Have you checked for false spider mites? They are extremely small, usually attack the undersides of the leaves. They like it warm and dry, low humidity. Look on the undersides of the leaves, you might notice a "silvery sheen" to the leaf surface as you gently shift the leaf from side to side.

If it's not mites. It's probably blight.
I've heard that spraying with a mixture of :
3 Tbl baking soda
1 Tbl vegetable oil
2 Drops of regular dawn dishsoap
To 1 gallon water
Will slow progression down.

It's a soil Bourne disease.
Only cure is to solarize soil.

Are you using Roundup or another herbicide around the edges of your garden? Are only the outside plants affected?