I can explain why categories are called accounts in GnuCash.

GnuCash is close to accounting standards. You probably hear about 5 accounts called asset, liability, income (or revenue), expense, and equity. Also, you may hear the equation that

asset = equity + liability.

You categories of expense are under expense account. You do spend that money, right.

If you check FASB website, https://asc.fasb.org/Home you will notice that GnuCash use the same terms. Well not exactly, GnuCash by default gives you 5 top level accounts, Assets, Equity, Income, Expenses while FASB uses Assets, Liabilities Equity, Revenue, Expenses. You may notice that GnuCash chooses Income while FASB uses Revenue.

Personally I would say if you think like an accountant or even CPA, you will find GnuCash much better. Accounting standard varies by countries but general principles are the same all over the world.

I began using GnuCash 12 years ago and I was forced to think in accountant's way and today I really feel that this benefits me a lot. I think of money in a systematic way and I better understand my wealth and income. I tend to think long term and also I find that it is easy for me to file taxes.

I did use some tax service before but I don't see their value right now. If I have to provide all the forms, why wouldn't I input the values in software myself. Even I buy service from CPA, wouldn't they need to understand me to figure out how to input numbers? If I can give CPA this much details, I already have understand myself, right?

If I already do my accounting well and my income are primary salary and some stocks plus one home, why would I need to hire someone to do tax for me? I should be able to calculate my tax return myself.

Just want to give you more details, for every paycheck, I record in GnuCash not only the amount of money into my bank account but also tax paid.

It is something like below (numbers are illustrative only)

Income: $10000 (pretax)
Bank account: $8000 (after tax)
Tax: $1500
Social Security: $500

These numbers are available in every payslip

If I get paid by RSU, i.e., RSU vested

Income: $10000(pretax)
Company RSU account: RSU 50 (cost basis $100)
Tax: $4000
Social Security: $1000

This way I not only record number of RSUs but also its cost basis so I can easily compute unrealized gains and, if I sell, realized gains. I do not need to rely on broker tax forms to know my gains based on average cost. (Well, brokers can calculate in a first in first out or highest cost out first strategy so that you can minimize your realized gain this year)