Bard gets JOAT and can Inspire themselves.
Inspiring themselves is better than expertise (because it can be applied to far more skills or types of checks) and the lore bards need a new 14th level ability. Expertise instead keeps more simple and restricts the benefits to a few skills.
RIP bards, it must be so hard being a fullcaster and not getting expertise, you still get jack of all trades
The problem is bards need to have some appeal over a full caster to be worth playing. That appeal comes from:
- spell versatility
- bardic inspiration
- skill benefits
Spell versality is very limited because of the preparation mechanic bards use and the fact magical secrets doesn't exist until the third tier of play. That forces the player to be selective in spells prepared. If they're focusing on cleric spells it's better to be a cleric. If they're focusing on druid spells it's better to be a druid. If they're focusing on wizard spells it's better to be a wizard. There's no significant value that a bard has in casting spells that other spellcasters can already cast just as well or better, especially when bonus spells prepared favor other spell casters more and the relevant casters can all swap them out on a long rest.
Bardic inspiration can be useful but it's a class feature like wild shape, or channel divinity, or arcane recovery and ritual adept, or font of magic and metamagic, or invocations. As an alternative class feature bardic inspiration cannot compensate for the limited spell prep compared to most full casters when they also have their own class features. Most class features on other full casters are more appealing than bardic inspiration.
That brings us to skill benefits. The only skill benefits are a bonus proficiency, expertise, and jack of all trades. Jack of all trades is a minor benefit (usually in skills the PC isn't focusing), another skill proficiency is minor (further marginalized by jack of all trades), and you would remove expertise. Clerics have the thaumaturge option. Druids have the magician option. Wizards also have expertise. Bard expertise is better but in removing it the skill based spellcaster loses out comparatively to other spellcasters further. That's not useful.
Expertise is also the modern replacement for the classic bardic knowledge / lore abilities. A traditional bard in 5e terms should be taking expertise in arcana and history, but choice of skills expands on bard archetypes. Removing it should also be replacing it with a bardic knowledge ability in some relevant form.
When someone says "because full caster" in reference to a bard it's the equivalent of grouping rogues with barbarians, fighters, and paladins "because martial" as equivalent then claiming rogues don't need expertise as a full martial because martials are good at soaking up and dealing damage. Statements like that ignore the differences in those classes and context behind those differences. Which is a bit ironic in a thread about rangers.
Expertise is a more restrictive solution than self-inspiration, maintains a method for the classic bardic knowledge or other archetypes, and helps give a reason to play bards over other spell casters in the first place. It's in the right place on bards.