The Ring protected itself. Each person who saw the Ring was drawn to it, sometimes quite out of character.
Isildur took the Ring from Sauron's hand and, even though he knew what it was and what harm it had done and with Elrond counselling him to destroy it, could not bear to destroy it which, physically, would have been easy, since they were already on the slopes of Mt Doom. He writes:
But for my part I will risk no hurt to this thing: of all the works of Sauron the only fair. It is precious to me, though I buy it with great pain.
Smeagol sees it and immediately lusts after it, kills his friend to get it and then hides in the mountains for many centuries muttering about his "Precious".
Bilbo was nearly unable to give it to Frodo (even with Gandalf's help). Destroying it would have been much harder.
The Ring takes over:
And if he often uses the Ring to make himself invisible, he fades: he becomes in the end invisible permanently, and walks in the twilight under the eye of the dark power that rules the Rings. Yes, sooner or later - later, if he is strong or well-meaning to begin with, but neither strength nor good purpose will last - sooner or later the dark power will devour him.'
He said that [the Ring] was "growing on his mind", and he was always worrying about it; but he did not suspect that the ring itself was to blame.
A Ring of Power looks after itself, Frodo. It may slip off treacherously, but its keeper never abandons it. At most he plays with the idea of handing it on to someone else's care - and that only at an early stage, when it first begins to grip.
And if it won't let itself be abandoned, it even more strongly resists being destroyed. Once he learns of the Ring's evil, Frodo asks Gandalf:
'But why not destroy it, as you say should have been done long ago?' cried Frodo again. If you had warned me, or even sent me a message, I would have done away with it.'
'Would you? How would you do that? Have you ever tried?'
'No. But I suppose one could hammer it or melt it.'
'Try!' said Gandalf. Try now!'
Frodo drew the Ring out of his pocket again and looked at it. It now appeared plain and smooth, without mark or device that he could see. The gold looked very fair and pure, and Frodo thought how rich and beautiful was its colour, how perfect was its roundness. It was an admirable thing and altogether precious. When he took it out he had intended to fling it from him into the very hottest part of the fire. But he found now that he could not do so, not without a great struggle. He weighed the Ring in his hand, hesitating, and forcing himself to remember all that Gandalf had told him; and then with an effort of will he made a movement, as if to cast it away - but he found that he had put it back in his pocket.
Gandalf laughed grimly. 'You see? Already you too, Frodo, cannot easily let it go, nor will to damage it. And I could not "make" you - except by force, which would break your mind.
When Sam and Frodo reach Mt Doom, Frodo is unable to destroy the Ring:
'I have come,' he said. 'But I do not choose now to do what I came to do. I will not do this deed. The Ring is mine!'
And after Gollum has destroyed it, he says:
'But do you remember Gandalf's words: Even Gollum may have something yet to do? But for him, Sam, I could not have destroyed the Ring.