Many can be the reasons, but to make it simple, it all comes down to energy expenditure.
When you want to lose body fat, you want to do so by 'eating as much as possible' and still lose bodyfat.
This means having the right ratio of energy expenditure : energy intake, in order to sustain the diet for longer.
Going out with friends, shopping, or any extra activity you can think of you're NOT doing now - all contribute to increasing and maintaining your *normal* metabolism.
Infact, NEAT (Non Exercising Activity Thermogenesis) is most likely the biggest variable that determines our TDEE.
If you're in Italy (like me), asides from training, you're also doing much less other activities, which all contribute to an overall energy expenditure.
This decreases the energy expenditure variable, making this period not optimal for you to diet.
Can it be done?
Sure. A caloric deficit will work regardless.
Should you be doing it ? It depends. I'll give you my own advice based on my experience and knowledge.
Personally I don't think it's the right time to diet because of 6 reasons. If you're spending more time at home:
1) your energy level is low.
2) this means you need less calories to sustain your current bodyweight.
3) staying more at home can lead to eating more food out of boredom.
4) dieting would probably result in very little calories eaten everyday, which could lead you to think of your next meal for most of the day
5) Not to mention that if you don't have access to a gym, it would be much easier for you to lose muscle mass too, decreasing your overall TDEE and overall size.
I would personally advise to spend this time at maintenance, probably gain a tiny bit of body fat, preserve more muscle mass and train with what you can.
What are your thoughts on the matter?