Why must I sign in every time I come here?

It is most likely caused by your internet browser deleting or not retaining the web site cookies. When you sign in, cookies are installed in your browser so the web site can recognize your account by the cookies.

Below is an article from Yahoo Help explaining why you have to sign in again:

http://help.yahoo.com/kb/index?y=PROD&page=content...

My suggestion is to check the privacy settings of your internet browser to make sure it accepts cookies and not deleting them on exit. Also, clear the cache to fix as the browser is storing the information in your old page so it continues requesting you to sign in again..

For internet explorer, click the gear looking icon near the right upper corner of the page and select internet options. A pop-up dialogue box should appear. Click delete under browsing history and start deleting old cookies.

See the following article from Yahoo Help for details:

http://help.yahoo.com/kb/index?y=PROD&page=content...

Please also make sure the box of deleting history on exit is unchecked. Click the privacy tag and then the "Advanced" box. The box next to accepting first party cookies should be checked. If the above does not correct the problem, you may reset the explorer by clicking advanced tag in the internet option pop-up dialogue box and click "reset" under reset internet explorer.

For the other browser like firebox or chrome, click the settings/options icon usually located near the right upper corner or the left upper corner. Choose the privacy tag to check the cookie settings.

Last thing is to try installing a new different browser and sign in into your account to see if you need to sign in repeatedly with the new browser.