Hypothyroidism - hormones

I understand that TSH is released to stimulate the thyroid to release T3/T4 and that creates a negative feedback loop.

However, in hypothyroidism TSH is high but T3/T4 is low. Why is that? If TSH stimulates the release of T3/T4 then shouldn't there be more of the hormones in the blood when TSH is high?

What is stopping the TSH from stimulating more release of the hormones?

just speculating here but maybe some kind of abnormality in the TSH receptors so TSH can't activate the release of T3/T4?

googled it and NHS says the main cause is autonimmune attack of the glands which prevents release of T3/T4