Higher Level Spells: Why such a lack of variety?

I am a DM and my campaign is nearing its conclusion with the characters currently being 13th level. 4 out of my 5 PCs are spellcasters, and the players are really imaginative when it comes to spellcasting and using spells in unexpected ways. Or at least that was the case in lower levels. Now that they have access to high level spells I have noticed that the spell variety is incredibly limited. Nearly all of them are Evocation/Transmutation/Conjuration and most of them deal damage. Some of the more interesting schools like Divination, Illusion and Enchantment are pretty much nonexistant and or extremely situational.

So, what are your solutions to this issue? Do you use any homebrewed spells that are more flavourful high level options?