Two possible reasons come to mind:
1) you need to use loot tables now. eg https://github.com/TheGreyGhost/MinecraftByExample/tree/master/src/main/resources/data/minecraftbyexample/loot_tables/blocks
2) you're mining in creative mode
-TGG
With the migration the WYSIWYG editor no longer has a button for in-line code (teletype).
Several other buttons may have also been lost, but TT was the only one I used regularly.
Example (link preview doesn't display it, but LootModifierManager is formatted as inline code):