Blocks added in 1.12 (specifically concrete & glazed terracotta) have a noticeably lower blast resistance compared to similar blocks (stone, cobblestone, bricks, terracotta, etc). Not only that, but they're some of only a very few blocks with unique blast resistance values (the others being cobwebs, hoppers, & ender chests), but I've only just recently discovered the reason. All blocks added in 1.12, the World of Color Update, have their blast resistance set to the same value as their hardness. This also shows why concrete powder (the only other block added in the update) doesn't seem to have this problem, as it has roughly the same hardness & blast resistance as both gravel & sand. Here's a table for easy comparisons:

1.12 Added	Block	Blast Resist.	Hardness
	Concrete	1.8	1.8
	Stone	6	1.5
	Cobblestone	6	2
	Glazed Terracotta	1.4	1.4
	Terracotta	4.2	1.25
	Bricks	6	2
	Concrete Powder	0.5	0.5
	Sand	0.5	0.5
	Gravel	0.6	0.6

Now, in case it wasn't clear why this is a problem, ghasts are able to destroy blocks with a blast resistance of ~3 or less, and since 1.16+ now encourages building more in the nether, this problem becomes much more apparent.

I do suppose a case could be made for glazed terracotta possibly being more fragile than regular terracotta, as it is more of a detail oriented block, but that's also why I included bricks as a comparison, as they're both made almost the same way and with the same ingredients. All things considered, glazed terracotta should probably have a blast resistance of 4.2.

Concrete, on the other hand, has no reason for being not only over 3 times less resistant than stone, but also less resistant than logs (B.R. of 2), planks (B.R. of 3), and even bone blocks (B.R. of 2). Concrete should have a blast resistance of 6, given the blast resistance of similar blocks.