Most creatures are summoned unwillingly, or are otherwise unhappy about being summoned.
The Monster Manual is rife with examples of creatures that hate being summoned, under almost any circumstances. For example:
Devils: MM (67):
However it is summoned, a devil brought to the Material Plane typically resents being pressed into service. However, the devil seizes every opportunity to corrupt its summoner so that the summoner's soul ends up in the Nine Hells. Only imps are truly content to be summoned, and they easily commit to serving a summoner as a familiar, but they still do their utmost to corrupt those who summon them.
Yugoloths (a specific circumstance) (MM 311):
A yugoloth summoned using its true name, as inscribed in the Books of Keeping, is forced to serve its summoner obediently. The yugoloth hates being controlled in this manner and isn't shy about making its displeasure known.
Elementals (MM 123):
Certain spells and magic items can conjure an elemental, summoning it from the Inner Planes to the Material Plane. Elementals instinctively resent being pulled from their native planes and bound into service. A creature that summons an elemental must assert force of will to control it.
Demons (MM 53):
A mortal who learns a demon's true name can use powerful summoning magic to call the demon from the Abyss and exercise some measure of control over it. However, most demons brought to the Material Plane in this manner do everything in their power to wreak havoc or sow discord and strife.
(MM 51):
If a single mistake is made, a demon that breaks free shows no mercy as it makes its summoner the first victim of its wrath.
One exception is a Glabrezu (MM 53):
A glabrezu takes great pleasure in destroying mortals through temptation, and these creatures are among the few demons to offer their service to creatures foolish enough to summon them.
The Gate spell is explicit about simply pulling any creature away without notice:
When you cast this spell, you can speak the name of a specific creature (a pseudonym, title, or nickname doesn't work). If that creature is on a plane other than the one you are on, the portal opens in the named creature's immediate vicinity and draws the creature through it to the nearest unoccupied space on your side of the portal. You gain no Special power over the creature, and it is free to act as the DM deems appropriate. It might leave, Attack you, or help you.
The Conjure Fey spell implies that the fey resents being summoned, since it attacks you if you lose concentration (much like a demon):
If your Concentration is broken, the fey creature doesn't disappear. Instead, you lose control of the fey creature, it becomes hostile toward you and your companions, and it might Attack.
Confusingly, the Conjure Woodland Beings spell does not have that clause. Indeed, you could summon the same creature with either spell, and it will only attack you when you lose concentration only if you used the higher level version.
The only case that might allow for some free will is Conjure Celestial, because it has the freedom to only obey commands that follow its alignment.
It obeys any verbal commands that you issue to it (no action required by you), as long as they don't violate its alignment.
No, casting Compelled Duel would end the Sanctuary effect on you.
As you quote:
If the warded creature makes an attack or casts a spell that affects an enemy creature, this spell ends.
Compelled Duel is a spell which affects an enemy creature, being cast by the warded creature (you), so it causes the sanctuary effect to end.
You can do it the other way around though
If you cast Compelled Duel and then have Sanctuary cast on you, the effects can overlap. A target successfully affected by Compelled Duel would have disadvantage on attacking anyone but you, but would be forced to make a wisdom save before they could attack you.
Note that the Wisdom save that Compelled Duel mentions happens only once, when you actually cast the spell on them. They either succeed, and therefore shrug off the effect and can act as normal, or they fail, and thus suffer disadvantage on attacks against other targets for the duration of the spell. The subsequent wisdom saves the spell may cause are only to do with the affected creature's movement - it still has disadvantage on attacks even if it successfully manages to move away from you (though you must remember to chase after it yourself if you don't want the effect to end).
Best Answer
The elemental doesn't become indifferent against its previous targets. It was indifferent. The only thing that made it attack the target was the caster's will. Now, when the caster's concentration is broken, their will enslaves the elemental no more.
The elemental is angry toward the caster, who pulled it out of its plane. It even might attack the caster or one of his/her allies. But nothing in the rules says it must (or will) attack. What the elemental will do is up to the DM.