I was surprised by how many Xanathars spells didnt make the cut into 2024. Even old school elemental spells like Pyrotechnics are now only in Xanathars.
A main consideration seems to be whether the spells were mostly redundant with the spells that are already in the 2014 Players Handbook. So, if Fear already exists, why add Cause Fear? Only spells that added something new and interesting seem to make the cut.
Some earlier 2014 spells seem to update by absorbing aspects of an unselected spell, like Chromatic Orb now randomizing analogous to the left out Chaos Bolt.
Happily, the subpar spells from Xanathars were left out.
Tensers Transformation stayed out, but this probably relates to martial/caster disparity.
Some missing Xanathars spells surprised me, like slot 9 Invulnerability, which is a decent and distinct option.
Some "psionic" spells, like Tashas Mind Whip and Intellect Fortress, also didnt make it, which made me think they might be saving these for a future Psion caster class.
I wish the 2024 Players Handbook left out some of the spells from the 2014 Players Handbook. Heh, certain spells like Hallucinatory Terrain and Mirage Arcane are so offensively worthless they pollute the valuable page space of the new book. Meanwhile, even many old school players dont seem to realize that 5e skills have completely obsoleted certain spells, such as the History skill making Legend Lore pointless. Similarly, Telepathy related spells have stupidly high slots, when these features are fine for a species trait of a level 1 character, and work fine as a slot 2 spell. It would be better to leave these spells out rather than reprint them with their unworthy spell descriptions. If designers rethink one of these worthless spells, a future splatbook can publish it with its new description.