Going back into history, we can take this ancient tradition of temple gatekeepers to village guardians in ancient indian times which goes straight to the Yaksha cult. They have been through a couple of political cult changes along the way both buddhist as well as shaivite before they entered into a phase where they were finally defined as "Dvarapalas" in temple architecture.
The earliest creative examples of a decent dvarapala as we know it were carved by Baladeva, a chalukyan sculptor who belonged to a guild or artists who indulged in temple architecture around Aihole Badami and Pattadakkal. These artists did various things, for example, one sculptor was responsible for just the jali windows that adorn closed mandapas in temples. Another sculptor just carved ceiling panels for the great rulers depending on which cult the temple was to be dedicated. Yet another carved only lintels and assisted in planning on how all this was going to be put together and hoisted up to form the final structure - a temple in dravida or nagara style.
Lets take Baladeva. He specialised in dvarapalas, making them lean on the pillar and hold a club during his time. So if he were to dedicate a dvarapala to a shaivite temple he would give the dvarapala the same pose, but add a club to his hand and a third eye to his forehead. During his time, dvarapalas were incidentally human size and normal, soldier like. What happened with his contemporaries in the south was a little different. The pallavas also made them, some fierce, some gentle holding lotuses in their hands and inviting you home, for a cup of tea maybe. They were slender in true Pallava style.
Now came the big imperial guys, the Cholas who wanted to really show they are BIG. Their dwarapalas were giant size, snarled down at you making you feel real small when you entered the Brihadeshwara temple for example, or even larger and fierce when you tried to enter Gangaikondacholapuram temple. The are true giants, massive with fangs towering up and leaning on the walls leading up to already high cielings showing true Chola imperialism in their art. They also had a yali accompanying them at the bottom.
Back again during the late chola early vijayanagara time they became shade smaller, but more ornate, didnt lean on anything but stood kinda cross legged, this time with sharp fangs. Now they were demons for all practical purposes with a "dare not enter" look to their faces. The nayakas had learnt the art of chiseling stone very well and got the dvarapalas their muscles in better shape with more ornate jewellery to suit their rich exterior.
Finally, Marunthiswar Shiva temple at Thiruvanmiyur, brought about a drastic shift in the thought process of the generation of people who learnt temple architecture in their time. The same dvarapala, never shall die, the same pose, the same club, the same fangs but without any sign of the lost Chola imperialism in their form. They cover all of 10 by 10 inches of the gateway that leads into this temple. Crisp sculpture i should say, just so small that you have almost missed the dvarapala in the act of guarding the temple gate.
So much for a dying practise of guarding the diety. The dying of not just the dvarapala himself, but the very idea with which he even took birth in the Indian architects mind. He will always remain there, just ignored, unwanted, and forgotten...