Look at the source of wealth.
Until Rome took over Egypt after 80 BC, Egypt had dominated trade between eastern mediterranean and Indian Ocean rim - a lot of small bulk but highly expensive stuff was traded from the Silk Routes and India / China / eastern Africa, up the Red Sea via Egypt. This position was gradually lost because of successive political turmoil but especially as the Ottoman Empire lost these trade routes to Venetian thuggery.
The later Ottoman empire also did not stop foreign interests such as Britain and france from helping themselves to their land, heritage and economy - the Suez canal was built through Egypt and did not profit the country till the Suez crisis.
In the 20th century Egypt has still been caught between world powers with the USSR and the USA vying to have a foothold in the country.
http://www.cnn.com/SPECIALS/cold.war/kbank/pro files/sadat/
To overcome a legacy of decline requires international aid but when this aid comes with strings attached the long-term position is dodgy, and without peace and stability you don't get prosperity. The next biggest threat is that muslim extremists give the current regime the excuse to remain repressive.
Thing is, Egypt is still very rich agriculturally (though not in an agrinomics sense) and although you see a lot of poverty I haven't seen hungry people - and many ordinary people exhibit despite all the above a happiness with home and family that 'rich' countries might envy.