I think you're generally wrong on the "they have not been doing" comment. Israel has been giving warnings, and those warnings were intentionally being ignored to maximize the damage to Israel's reputation. But if you have some comprehensive data here I'd be interested in seeing it.
From my observation the pattern has been Israel giving warnings/ordering evacuations with the response being "it can't be done" only to end with significantly more difficult conditions.
Israel did demand that the entirety of Northern Gaza be evacuated from civilians (including those "camps" you mention, more below, and including all those hospitals) which was again pushed back on as "impossible" or physically prevented by Hamas which in turn caused increased civilian casualty rates and the eventual almost full evacuation under significantly more difficult conditions.
The use of the terminology "refugee camps" is also confusing. Some of what the media refers to as "refugee camps" are permanent settlements, effectively cities, where the population consists of many 1948 refugees. Not what most people think about when they hear "refugee camps". As to why heavy bombs are used I'm not an expert but potentially to penetrate deeper and there might be other reasons.
All that said, I think it should be acknowledged that some of the methods Israel is using are likely to try and achieve some psychological advantage against the enemy. I don't think this that's necessarily a violation of international law given that warnings were given. It's within the realm of what I would call a military objective (demoralizing the enemy forces and destroying their infrastructure).