It is recommended for whoever intends performing Qurbani, to abstain from cutting ones nails and hair as was mentioned by Rasūlullah ﷺ “When the ten days (of Dhul Hijjah) commence and a person has a sacrificial animal, which he intends to slaughter, then let him not cut his hair or pare his nails.” (Muslim)
قال إذا دخل العشر وعنده أضحية يريد أن يضحي فلا يأخذن شعرا ولا يقلمن ظفرا
(مسلم رقم الحديث 1977, دار إحياء التراث العربي)
Rasūlullah ﷺ did not mention the exact reason why a person should not cut his hair or nails; therefore, any explanation for its underlying reason is mere conjecture. Read more