The officials, speaking on condition of anonymity to discuss Ukraine’s war plans, cited three reasons:

Recent advances: For more than seven weeks, Ukrainian troops have fought along three main fronts across several hundred miles in the country’s east and southeast, pressing to find a weak spot in the heavily dug-in Russian defenses to burst through. They have been making plodding but steady progress clearing a path through dense Russian minefields and other fortifications.

Russian turmoil: Ukrainian forces sensed an opportunity with the sacking of the regional Russian commander, Maj. Gen. Ivan Popov, to exploit turmoil in the local Russian leadership. Last month, General Popov addressed his troops in a four-minute recording, accusing his superiors of inflicting a blow on his forces by removing him from his post in retaliation for voicing the truth about battlefield problems to senior leadership behind closed doors.

Potential Russian vulnerabilities: Ukrainian artillery barrages have been steadily attacking Russian artillery, ammunition depots and command posts in areas well behind the front lines, creating a vulnerability to exploit if advancing Ukrainian forces can punch through the Russian defenses, and cause havoc in the rear. “The Russians are stretched,” a Western official said on Wednesday, speaking on condition of anonymity to discuss operational details and intelligence assessments. “They are still experiencing problems with logistics, supply, personnel and weapons. They’re feeling the pressure.”

from:

https://www.nytimes.com/live/2023/07/26/world/russia-ukraine-news?smid=url-share#us-officials-describe-a-3-point-rationale-for-ukraines-new-push