Kyiv could conduct offensives right now, but they would be unlikely to achieve serious successes while sustaining losses. It makes more sense to wait for new equipment, trained units, better ground conditions, etc. for their big push, which will be more likely to achieve success.

Ukraine is clearly holding back reserves for its offensives later this year, which may give the perception that it is losing, but committing those reserves to the front now to defend would make them less effective for future offensives. It is a calculated risk. 2/

It is natural to go on defense after successful offensives. Slow grinding offensives are not in Ukraine's interests, so they need to give themselves the best chance for achieving a deep penetration of Russian lines that can be exploited. That requires greater forces/planning. 3/

Also important to emphasize that mobilization has given Russia a manpower advantage. Poorly-trained soldiers are of less value in offensive operations, but they have strengthened Russia's ability to defend and sustain the war, particularly in an attritional fight. 4/