Because the "I" still interferes with those meditative states. Do not hold on to self-identity and your meditation would go much smoother:
Bhikkhus, how do you conceive it: is form permanent or impermanent?" — "Impermanent, venerable Sir." — "Now is what is impermanent painful or pleasant?" — "Painful, venerable Sir." — "Now is what is impermanent, what is painful since subject to change, fit to be regarded thus: 'This is mine, this is I, this is my self'"? — "No, venerable sir."
"Is feeling permanent or impermanent?...
"Is perception permanent or impermanent?...
"Are determinations permanent or impermanent?...
"Is consciousness permanent or impermanent?" — "Impermanent, venerable sir." — "Now is what is impermanent pleasant or painful?" — "Painful, venerable sir." — "Now is what is impermanent, what is painful since subject to change, fit to be regarded thus: 'This is mine, this is I, this is my self'"? — "No, venerable sir."
"So, bhikkhus any kind of form whatever, whether past, future or presently arisen, whether gross or subtle, whether in oneself or external, whether inferior or superior, whether far or near, must with right understanding how it is, be regarded thus: 'This is not mine, this is not I, this is not myself.'
"Any kind of feeling whatever...
"Any kind of perception whatever...
"Any kind of determination whatever...
"Any kind of consciousness whatever, whether past, future or presently arisen, whether gross or subtle, whether in oneself or external, whether inferior or superior, whether far or near must, with right understanding how it is, be regarded thus: 'This is not mine, this is not I, this is not my self.' ~~ SN 22.59 ~~