Mostly because most of the people do not know about Nano.

Another thing is that the Bitcoin is used more as a investment rather than a actual currency

People don't use BTC except as an investment. Those with power and money control and make a lot of money from this. Nano will not allow them to do that. Look at the countries where their population are somewhat using Nano (ex. Venezuela). Do you think the world powers want them to be economically independent from them? People do know about Nano. The ones with power are just not talking about it.

Because they don't realize how good nano is

Yes because it's make it easier

NANO:,it's the lowest level in history.the price is low

Bitcoin is one of the first cryptocurrency so think of it as an investment.
Like US dollar is taken as a standard for physical currency exchange and so just like that bitcoin is a standard between cryptocurrency exchange.
Nano being a currency not popularized and fee-less it much better to invest in it

For a series of reasons. One of which is that bitcoin started 6 years earlier than nano and it managed to impose itself as a standard. The story of technologies who became a standard show us that there are so many factors that make it almost impossible to predict what will become a standard. VHS as an example wasn't the best technology, yet it became a standard and killed every other video-tape technologies. Once people recognise something as the standard the network effect locks users into it. The good news is that Bitcoin is becoming the standard in storing value, Nano can still be the standard for payments.

for cleaning black money

We should bug the big YouTubers in the crypto niche to talk about NANO and why it is so ignored! If one of the big guys talks, everybody will follow.

it's simply because Bitcoin is the first crypto currency and it controls other alternate coins

Bitcoin is more acceptable by many merchants worldwide, its has more liquidity than Nano

because bitcoin is first crypto currency and has higher rates than other crypto currency it has many exchange available with giftcard or cash

Because users are able to send and receive bitcoins with only a smartphone or computer, bitcoin is theoretically available to populations of users without access to traditional banking systems, credit cards and other methods of payment.

1- They do not know NANO
2- They know NANO, but they believe that Bitcoin has bigger upside than NANO
3- They know NANO, but they believe it is too good to be true
4- They are in denial, they have invested so much on Bitcoin and they have fear to flip their investment to NANO, because Bitcoin is more popular
5- They are simply too stupid to search for alternative cryptos with no fees or better fundamentals than Bitcoin, because they are maximalists

Like myself, I think most people are unaware of the numerous other currencies.

good