Being able to sit on ones heels is a fundamental mobility requirement for all humans. This position is particular important for movement arts, such as jiu jitsu and yoga. There are many factors that may limit you: joint hypomobility, muscle length deficits, swelling, neural tension etc. Here are some self-mobility drills that you can do to improve your kneeling mobility.
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1️⃣End-range squat holds: squat as deep as you can and spend time at the bottom. If one knee feels tighter you can lean towards that side. Start with 20 second holds and build up to 2 minutes.
2️⃣Knee joint mobilization: by using a towel or a soft object between the thigh and calf you will anteriorly translate the tibia forward to stretch the joint capsule. This should be comfortable and pain-free. Avoid if you have ligament laxity.
3️⃣Kneeling PAIL/RAIL: kneel to your end range and hold for 1-2 minutes. Alternate with isometric contraction of your quads then try to sit deeper in the position. Perform 10 second isometric holds and keep going until you aren’t making any more progress or if it becomes painful.
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As a rehabilitation specialist and a martial artist I feel it is unacceptable to be content with inadequate mobility.