Why do insomnia increses the blood pressure?

Physiologic anxiety: Sleep deprivation is often associated with anxiety which is accompanied by physiological responses. It is likely part of the stress response.

See below: Prolonged insomnia is stressful to one's emotional and medical well-being. One physical manifestation, amongst many, of stress is changes in blood pressure. Also, insomnia can result from a large variety of medical/mental health conditions, and/or lifestyle (eg dietary/exercise) choices many of which can lead to increased blood pressure especially if untreated.

Insomnia: Transient & related to sleep deprivation which results in elevation of adrenaline which raises blood pressure.