Because the sessions use a cookie to hold the session id, which then subsequently get transferred on each request back to the server.
Domain webci.com and weblara.com are two separate domains, so they can't read each others cookies.
If it was setup like ci.domain.com and lara.domain.com (subdomains on the same domain), then they could read each others cookies if you set .domain.com as the cookie domain in /config/sessions.php